Reasons why each shootings happened

Shooters
Charles Whitman
Insanity.
In 1966, Whitman discussed his health concerns with University doctor, Jan Cochrun, who prescribed Valium and recommended he visit campus psychiatrist Maurice Dean Heatly. By the summer, Whitman was prescribed Dexedrine. it was revealed during the autopsy that Whitman had a cancerous glioblastoma tumor in the hypothalamus region of his brain. Some have theorized that it may have been pressed against the nearby amygdala, which can have an effect on fright/flight responses. This has led some neurologists to speculate that his medical condition was in some way responsible for the attacks, as well as his personal and social frames of reference.

Edward Charles Allaway
Insanity.
Five different mental health professionals diagnosed him with paranoid schizophrenia. He presented a history of mental illness. He was committed to the California state mental hospital system, where he remains at Patton State Hospital in San Bernardino, as of 2007

Brenda Ann Spencer
Possible insanity / influence of drugs
The school was across the street from Spencer's house. She used a rifle that she had recently been given for Christmas by her father. When the six-hour incident ended and she was asked whom she wanted to shoot, she said, "I like red and blue jackets". When asked why, she shrugged and replied, "I don't like Mondays. This livens up the day."She also said, "I had no reason for it, and it was just a lot of fun"; "It was just like shooting ducks in a pond"' and "[The children] looked like a herd of cows standing around; it was really easy pickings." At the time of the shootings, Brenda Ann Spencer was 16 years old.
In 2005, she claimed that she was drunk and under the influence of PCP, and that her father, Wallace Spencer, had sexually abused her as a child and that the state and her attorney conspired to hide her drug test results.

David F. Lawler
Lawler brought two family-owned pistols to the school in a blue duffel bag. He had received the ammunition for the shooting as a Christmas present.

Patrick Purdy
Insanity / Influence of Prescription Drugs
During the two years prior to the murders of the Stockton children, Purdy had been treated by psychiatrists who put him on the mind altering drugs Thorazine and Amitriptyline.

Gang Lu
Jealousy.
Months before the shootings, he wrote five letters explaining the reasons for his planned actions. According to university officials, four of the letters are in English and were intended to be sent to news organizations. One is in Chinese. The letters have not been released to the public. According to the university, Lu said in the letters that he was angry and jealous that his doctoral dissertation had not received a prestigious academic award. Linhua Shan, another student, had received the award.

Eric Houston

Wayne Lo
Loner / Socially unaccepted / Possible Hate crime /
Lo did not adjust well to the liberal college environment of Simon's Rock. Lo held views which were deemed racist, homophobic and anti-semitic by fellow students at the college. Lo steadily became more and more excluded by his fellow students.

Jamie Rouse

Barry Loukaitis
Unstable Mental condition, depression / frequently bullied in school / Possible influence of prescription drug
When Loukaitis was young, his father began an affair and his mother became increasingly distant and often spoke of suicide. She frequently implied that Barry would also have to kill himself, and had informed him that the date of the double-suicide would be on Valentine's Day of 1996. He had also suffered from clinical depression, a mental illness present in the last four generations of the Loukaitis and Phillips families. Loukaitis was widely believed to be frequently bullied in school, which impelled him to cause the murderous school rampage. Those who knew him claim that he complained of being beaten by other students, being sexually harassed, having his head repeatedly stuffed into toilets, and being held down while another student urinated on him. He was also taking Ritalin at the time of the shooting.

Jillian Robbins

Evan Ramsey
Lack of parental figures, guidance / Domestic Violence / Bullied at school / Unstable mental condition, depression
Ramsey's father was sent to prison when he was seven, and then his mother slipped into alcoholism. Ramsey and his siblings were then sent to foster homes, and in at least one he was sexually abused. Often, his own foster brothers would pay other students to beat him up as a sick game. He suffered from depression from as young as 10 and was contemplating suicide five years before the shootings. Ramsey was reportedly picked on frequently at school.

Luke Woodham
Possible Insanity / Influence of Satanism / Influence of prescription drug
Published reports say he was on Prozac. Minutes before his rampage, he gave a message to his friend stating that I killed because people like me are mistreated every day. I did this to show society, push us and we will push back. ... All throughout my life, I was ridiculed, always beaten, always hated. Can you, society, truly blame me for what I do? Yes, you will. ... It was not a cry for attention, it was not a cry for help. It was a scream in sheer agony saying that if you can't pry your eyes open, if I can't do it through pacifism, if I can't show you through the displaying of intelligence, then I will do it with a bullet." He pleaded insanity, but the jury rejected the insanity defense and instead found him guilty. During the trial, Woodham admitted to being a Satanist, and that he got the idea to commit the murders after his involvement in Satanism. According to Woodham, his friend Grant Boyette invited Woodham to join his Satanic group, known as "the Kroth."

Michael Carneal
bullied at school /
Because of his small frame, Carneal was frequently bullied. He would bring items to school and sell them in an attempt to make friends. Carneal's name was published in a middle school paper gossip column claiming that he had feelings for another male student. This led to name-calling, with students using names that referenced his supposed homosexuality. Carneal was reportedly on Ritalin. Weeks before the incident, Carneal stole a .38 handgun from his parents' room and attempted to sell it. A student took the gun, threatening to tell police if Carnael didn't give it to him. The student promised to pay Carneal later, but never did. In the weeks before the shooting, Carneal stole several firearms from both his own home and a friend's home. In early 1999, the parents of three victims represented by Jack Thompson filed a $33 million lawsuit against two Internet pornography sites, several computer game companies and makers and distributors of the 1995 film The Basketball Diaries. They claimed that media violence inspired Carneal and therefore should be held responsible. The case was dismissed in 2001. The 6th U.S. Circuit Court of Appeals ruled that it was "simply too far a leap from shooting characters on a video screen to shooting people in a classroom."

Mitchell Johnson & Andrew Gordon
Possible influence of prescription drugs
From Jon Rappaport of the Truthseeker foundation: http://www.nfgcc.org/schoolviolence.htm A Doctor from Georgetown University commented on Network television that one of the boys had previously been treated for violent behavior.According to one report, the boys were believed to be on Ritilan. Guns were stolen from Golden's grandfather's house

Andrew Jerome Wurst

Kipland Philip Kinkel
influence of prescription drug
Kinkel had been prescribed both Prozac and Ritalin and had been attending “anger control classes”. Kinkel had a strong interest in guns and bombs from an early age. His father at first resisted this, but later signed his son up for gun safety courses, and bought him a .22 caliber rifle and eventually a 9mm Glock handgun. Expelled from school for possession of gun on school ground. Killed parents then went to school the next day and killed people.

Shawn Cooper
Cooper had been taking Ritalin when he fired the shotgun's rounds and was reported to be on a mix of antidepressants.

Eric Harris & Dylan Klebold
influence of prescription drug / fascination of previous terrorism, Oklahoma bombing
Eric Harris had been taking an antidepressant when he killed twelve classmates, a teacher and wounded 24 others before taking his own life in the bloodiest school massacre in history. Toxicology reports confirmed that Luvox, an antidepressant, was in Harris’ system. He had previously been on Zoloft. Harris was a fan of musical groups such as Rammstein, KMFDM, Orbital, and The Prodigy. Soon after the shooting, KMFDM posted material on their website condemning Harris and Klebold's violence and denying that their music had anything to do with it. Most notably, Marilyn Manson, whose group the boys didn't listen to, was scorned viciously by the media immediately following the attack. Because Harris and Klebold were both underage at the time, Robyn Anderson, an 18-year-old Columbine student and old friend of Klebold's, made a straw purchase of two shotguns and Hi-Point 995 Carbine for the pair.[14] Anderson was not charged for her part in the straw purchase in exchange for her cooperation with the investigation that followed the shootings. After illegally acquiring the weapons, Harris and Klebold sawed off the barrels of the shotguns, shortening the overall length to below 25 inches, a felony under the National Firearms Act. they wished to "outdo" these events. They mentioned how they would like to leave a lasting impression on the world with this kind of violence. In his journal, Harris mentioned his admiration of what he imagined to be Darwinian natural selection. He wrote that he would like to put everyone in a super Doom game and see to it that the weak die and the strong live. On the day of the massacre, Harris wore a white T-shirt with the words "NATURAL SELECTION" printed in black.

Thomas Solomon Jr
influence of prescription drugs / unstable mental state / jealousy over a girlfriend
CNN Reports That T.J. Solomon was on Ritalin. from his stepfather's gun cabinet. He had access to higher powered guns but for some reason these were the guns that he chose to use to kill. Dr. Eddy Regnier, a teacher of psychiatry at Harvard University and who was hired by defense attorneys to examine T.J. said that T.J. had suicidal thoughts and believed to hear voices giving him commands. “He heard voices telling him to do strange things, but they were robotic voices, not human voices,” said Dr. Regnier. “On the one side is this really nice guy, but on the other side is a kid harboring angry feelings, who had made two suicide attempts, who spent his time thinking of death. He’s bringing guns to school. He’s talking to friends, and what are they talking about? ‘I’m going to shoot you.’” T.J. talked about shooting people at school and showed off the guns his stepfather kept in the basement. One possible motive for the shooting was the breakup between him and his girlfriend. Another motive might've been revenge. Some of T.J.'s friends spoke of his resentment of Jason Cheek, a popular boy two years older who had lettered in three sports.

Dedrick Owens
Derrick Owens found a .32-caliber handgun in his uncle's home.
Charles Andrew "Andy" Williams Williams felt he was targeted for physical and emotional bullying in school. In an attempt to fit in, he began to spend time with a crowd of skateboarders. Williams was accepted within this peer group; however, at times, these individuals also teased or picked on him.

Jason Hoffman
influence of prescription drug / unstable mental condition
Jason Hoffman, at age 18, was on Effexor and Celexa, both antidepressants, when he wounded two teachers and three students at California's Granite Hills High School. Hoffman had also undergone an "anger management" program. He later committed suicide, hanging himself in his jail cell.

Former student 43-year-old, Peter Odighizuwa
Academic problems / Odighizuwa had withdrawn voluntarily due to poor academic performance.

James Sheets

Biswanath Halder
vengeance
62 year old former student vengence Halder accused Shawn Miller, a computer lab administrator, for hacking into his computer

John Jason McLaughlin
bullied
At his murder trial, it was claimed that McLaughlin had intended only to wound Bartell, whom he thought had been teasing him, by shooting Bartell in the shoulder. Rollins was supposedly not his intended target.

Jeffrey Weise
influence of prescription drugs / unstable mental condition
He was on 60 mg. of Prozac a day. He obtained a pistol from unknown source, killing his grandfather with it, then stole his grandfather's police-issued weapons. No motives, but his flash based animations show his violent behaviors.

Kenneth Bartley Jr.

James Newman

Duane Roger Morrison
Sexually assaulted girls

Eric Hainstock
bullied
Reports indicate Hainstock was repeatedly attacked and bullied by homophobic remarks. He perceived that teachers and the principal did nothing to help the matter, and somewhat even took part in the bullying themselves. On the day prior to the shooting, the school principal John Klang gave Hainstock a disciplinary warning for having tobacco on school grounds.

Charles Carl Roberts
He fantasized about molesting little kids. He confessed to his wife that he's guilty of molesting his relatives twenty years ago. He left suicide notes before the shooting.

Seung Hui Cho
influence of prescription drugs / mentally ill / vengeance towards unspecified / hatred against the riches
On June 12, 2007, Cho's family released his medical records to the panel, although the panel said that the records were not enough. The panel obtained additional information by court order. Like the perpetrators of both the Columbine and Jokela school massacres, Cho was prescribed the antidepressant drug Prozac prior to his rampage, a substance suspected by Peter Breggin and David Healy of leading to suicidal behaviors. The toxicology test from the official autopsy later showed that neither psychiatric nor any kind of illegal drugs were in his system during the time of the shooting. He bought his guns. He had been diagnosed with and was treated for a severe anxiety disorder in middle school and continued receiving therapy and special education support until his junior year of high school. While in college in 2005, Cho had been accused of stalking two female students and was declared mentally ill by a Virginia special justice

Loyer D. Braden

Asa H. Coon
no known motive
The shooting was prompted by Asa Coon being suspended for fighting with another student on the subject of God on the Monday two days before, in which he was reportedly saying "Fuck God!" and that Marilyn Manson is actually God.

Latina Williams

Cornelius Cheers

Brandon McInerney
hate crime / bullying / influence of domestic violence
McInerney's home life was also troubled, marked by domestic violence. His mother Kendra pleaded no contest to being under the influence of a narcotic, and she had a record of methamphetamine use. In 1993, Kendra alleged that her husband Bill shot her in the arm. In another incident, Bill McInerney pleaded no contest and served ten days in jail and 36 months' probation on a charge of corporal injury to a spouse after he choked his wife almost to unconsciousness after she accused him of stealing ADHD medication from her older son. Between 2000 and 2001, McInerney's father had contacted child protective services five times about concerns of the boy living with his mother. In 2001, he filed a restraining order against Kendra; by 2004 Brandon was living with his father as his mother had entered a drug rehabilitation program. Brandon's grades began dropping, and he became disruptive at school. McInerney shot King twice in the head using a handgun he took from his backpack.

Steven Kazmierczak
possible influence of prescription drugs (withdrawal) / previous unstable mental history
He graduated from Elk Grove High School in 1998, during which he was treated temporarily for mental illness at the Elk Grove Village Thresholds-Mary Hill House psychiatric center. ABC News reports that his behavior seemed to become more erratic in the weeks leading up to the shooting, and that it is believed he stopped taking medication beforehand. His girlfriend, Jessica Baty, confirmed that Kazmierczak was taking Xanax (anti-anxiety), Ambien (sleep aid), and Prozac (antidepressant), all of which were prescribed to him by a psychiatrist. She said that he stopped taking Prozac about three weeks prior to the February 14 shooting. She also said that, during their two-year courtship, she had never seen him display violent tendencies and she expressed bewilderment over the cause of the rampage. "He was anything but a monster," Baty said. "He was probably the nicest, most caring person ever."

Jamar Siler