The Ciancias are a well-known family in a small town – Pennsville, Salem County, population 13,409. Ciancia's father, Paul Sr., runs an auto-repair shop and is prominent in his community, residents said.
Ciancia, 23, had few hobbies and outside interests, they said: Besides playing in the school band, he rode motorbikes or ATVs.
According to several accounts, his mother died from multiple sclerosis a year after his high school graduation, and he seemed deeply affected by her prolonged illness and death.
Ciancia kept to himself, Salesianum classmate Joseph Conti said, and he had few friends.
At school, Conti said, it was understood that Paul would join the family business instead of going to college.
Conti said he and Ciancia had several classes together - they sat next to each other because their last names were close in the alphabet.
He said Ciancia was mostly silent - except to let slip an occasional snarky comment about a teacher.
"But I've seen him smile and laugh before," said Conti, who is in law school.
Ciancia "never had a group," Conti said. He said band members would ask Ciancia to hang out from time to time but the trumpet player turned down their invitations. "He never was interested in any of that," Conti said.
After working in his father's repair shop for a time, Ciancia went to Florida. He graduated from the Motorcycle Mechanic Institute in Orlando in December 2011, a spokeswoman for the company that runs the school told the Associated Press.
In 2012, he went to Los Angeles, hoping for work as a motorcycle mechanic, the AP said.
A man who roomed with him in the Los Angeles area told ABC News that Ciancia had planned to return to New Jersey to spend the holidays with his family and "make amends with family problems."
On Friday, his family called the Pennsville Police Department, worried: Ciancia, they said, had sent a text message to his younger brother indicating he might harm himself.
Pennsville Police Chief Allen Cummings, a longtime family friend, called Los Angeles police, who drove to Ciancia's apartment to check on him.
By then, it was too late.
A federal prosecutor describing the murder charge filed against Ciancia on Saturday told reporters an assault rifle was used in the shootings. Ciancia was struck four times by police gunfire at LAX. He was reported to be in critical condition Saturday.
When searched, Ciancia had five 30-round magazines and "hundreds of rounds in 20-round boxes," a law enforcement official told the AP.
Investigators were still trying to determine a motive for the shootings. A federal law enforcement official told the Los Angeles Times a note found with Ciancia contained a rant against the government and the phrase "kill TSA."
In Pennsville, Paul Ciancia Sr.'s auto shop was closed Saturday, down the street from the family home, where police remained.
Officers took turns blocking the driveway with patrol cars. Residents drove by and snapped photos of the news vans clustered on the street.
Those who knew Ciancia were still dealing with the shock.
Conti said of his former schoolmate: "You had no idea what he was thinking. I never thought I would know anybody like this."