The 23-year-old suspect charged in the deadly shooting at Los Angeles International Airport was described as a loner by former classmates at his private, all-boys school in Delaware.
"He was kind of a shy guy. He always kept to himself, was always walking around by himself. Didn't really talk to anybody at all," former classmate Jeff Skidmore said of alleged shooter Paul Ciancia.
Ciancia graduated in 2008 from Salesianum School, a Roman Catholic school, in Wilmington, Del.
"Everybody in our senior class talked. There were few people that kept to themselves, and he was definitely one of them," Skidmore added.
Ciancia, who was shot by airport police, is under heavy sedation and monitoring at the Ronald Reagan UCLA Medical Center. He was dropped off at LAX Friday by a roommate who did not know what was about to happen, according to an official briefed on the case.
"He said he needed a ride to the airport to catch a flight, so he dropped him off," the roommate told ABC News.
The roommate is one of three who investigators have questioned. None of them were aware of Ciancia's intentions.
After Ciancia was dropped off, officials said he shot a Transportation Security Administration officer, Gerardo I. Hernandez, multiple times at point-blank range. As Ciancia advanced toward the checkpoint, the FBI says video surveillance shows he looked back and appeared to notice Hernandez was moving. Ciancia allegedly returned to shoot him again.
Ciancia is also accused of wounding two other TSA employees identified as James Speer, 54, and Tony Grigsby, 36. A teacher named Brian Ludmer was also wounded and remains hospitalized.
Federal prosecutors charged Ciancia with murder of a federal officer and commission of violence at an international airport. Both charges are potentially punishable by life in prison or the death penalty.
Ciancia graduated in December 2011 from the Motorcycle Mechanics Institute in Orlando, Fla., according to the school, before he eventually made his way to Los Angeles.
Ciancia once lived at the Rancho Los Feliz Apartments with former roommate John Mincey, who said he saw the suspect just last week.
"He said he was going back to New Jersey, going to work for his dad, making amends with family problems and spending the holidays with his family," Mincey told ABC News station KABC-TV.
Mincey said he was a roommate with Ciancia until last February.
"I mean I didn't have any issues with him or anything. He was a really nice guy. A bit of a loner, introverted," Mincey said.
The suspected gunman grew up in the blue-collar town of Pennsville, N.J., where his family still resides. Ciancia's father called Pennsville Police Chief Allen Cummings after he learned of his son's alleged role in the shooting.
"He called me and said, 'AJ, is this my son I'm seeing on TV? At the shooting at the airport?' And I said, 'Paul, I don't know. I just heard from a reporter the same thing," Cummings told ABC News Sunday night.
The other two TSA officers wounded in the attack have been released from the hospital. On Sunday, the TSA identified them as James Speer, 54, and Tony Grigsby, 36.
It wasn't clear why Ciancia targeted TSA officers, but what he left behind indicated he was willing to kill any of them that crossed his path, authorities said.
The shooter's duffel bag contained a handwritten letter signed by Ciancia stating he'd "made the conscious decision to try to kill" multiple TSA employees and that he wanted to "instill fear in their traitorous minds," FBI Agent in Charge David L. Bowdich said Saturday.
ABC News' Josh Margolin, Alexis Shaw and Anthony Castellano contributed to this report.