As early as age 10, Omar Mateen demonstrated a violent temper and lack of remorse in school that ultimately exploded in gunfire at Pulse nightclub in Orlando, Florida.

Born in 1986 to Afghan immigrant parents in Queens, New York, Omar Mir Seddique Mateen attended kindergarten at an Islamic school in Westbury, New York, before the family moved to Florida in 1991. While his grades in kindergarten indicated a need for academic improvement, Mateen began to slip behind once he was enrolled in public school in Florida. As he did, he became more violent.

By fourth grade, school officials said he was “academically behind [by] at least two years.” Mateen grew more violent the following year, when he hit a fellow student, according to school records that show he was disciplined for six other incidents. In seventh grade, teachers wrote that Mateen was disruptive and uttered obscenities.

That year Mateen was on track to fail English, science, and math, so a parent-teacher conference was called.

“Omar spoke only to his father in Farsi... and never addressed anyone else,” according to the teacher’s notes. “Omar is performing below average overall since he is unable to concentrate on his schoolwork and [he should] stop trying to get attention from his classmates.”

Mateen’s behavioral problems weren’t limited to being distracted.

“Hands all over the place—on other children, in his mouth,” his third-grade teacher wrote. Mateen was “verbally abusive, rude, aggressive,” and had “much talk about violence & sex (obscenities).”

Mateen occasionally showed a sensitive side, though.

“Dear Ms. Stein, I had a wonderful shimmering christmas holidy [sic],” he wrote to his third-grade teacher. “My gift was Bush Graden [sic] and unvesity studos [sic]. I missed you miss. stein on winter break.” He signed it “Love,” and his name spelled out from the O.

But by fifth grade Mateen took a sharp turn. Teacher Kathleen Zurich told his parents that he “lacks remorse,” can’t stay focused, and bounces around the classroom.

Mateen was disciplined 17 times that year, records show. Zurich told the New York Daily News that young Mateen acted out, and his former classmates said he even threatened to “kill everyone he didn’t like.”

He got much worse.

After Mateen transfered to a new middle school in eighth grade, he was suspended for 25 days. The next year, his freshman year in high school, he was suspended for 18 days. Five of those days were punishment for a fight in which he injured someone. After this fight in spring 2001, he was apparently sent to an alternative school.

Between eighth and 10th grade, Mateen was suspended for 48 days for fighting and other behavioral issues.

The final suspension recorded for Mateen came in the new school year, two days after the terrorist attacks of Sept. 11, 2001. Mateen was given a five day in-school suspension at the alternative school for an “other disciplinary violation” on Sept. 13.

Mateen’s life at home did not appear to be calm during this period, either. Shahla, his mother, was arrested in December 2002 for allegedly pinching her husband while he was trying to brush his teeth.

Later in his sophomore year, Mateen returned to Martin County High School. Mateen finished his education at Stuart Community Adult Learning Center in 2004.

After graduation, Mateen got an associate’s degree in criminal justice from Indian River State College and worked at a GNC nutritional supplement store. A former classmate and drag queen who worked next door at a Ruby Tuesday said Mateen was friendly to him and the restaurant’s other gay employees.

“He was a jokester and at the time didn’t have an issue with the LGBT community,” Samuel King told The Daily Beast.

In October 2006, Mateen was hired by the Florida Department of Corrections but was fired just six months later for not completing training.

In 2007, Mateen was hired by a private security firm, G4S, and passed its background check.

The firm learned in 2013 that the Federal Bureau of Investigation had questioned Mateen after claims that he made to co-workers about his own ties to terrorist groups. While the company didn’t dismiss Mateen, he was transferred to an unarmed position and subjected to another background check.

“We were not made aware of any alleged connections between Mateen and terrorist activities, and were unaware of any further FBI investigations,” G4S spokeswoman Monica Lewman-Garcia said in a statement to reporters. But apparently the FBI’s interest in Mateen was sufficient cause for the company to transfer him to a position where he didn’t carry a gun.

Mateen’s first wife, Sitora Yusufiy, said her ex-husband was not very religious, and it is unclear when and precisely how he was drawn to the terrorist cause. (Yusufiy said he routinely abused her before their divorce in 2011.)

Around 2013, Mateen is believed to have gotten married again, to Noor Zahi Salman, a California native whose parents are Palestinian. Salman reportedly accompanied Mateen on a trip to a gun store two days before the June 12 attack and is the subject of an FBI investigation. A federal grand jury has been reportedly convened to consider charges against Salman.