At around 9:30 Friday morning, 23-year-old Paul Anthony Ciancia reportedly stormed through a security checkpoint at Los Angeles International Airport’s Terminal 3 with a loaded AR-15 assault rifle. According to KTLA, on his way in, Ciancia shot and killed an unarmed security guard and wounded another TSA agent. He then walked towards the gates in Terminal 3, apparently stalking TSA employees while travelers fled and found shelter in stores, hid behind luggage and holed up in bathroom stalls.

Minutes later, police confronted Ciancia in front of a food court in the terminal. A brief gunfight ensued, during which police shot Ciancia several times, including in the leg and mouth. Ciancia is now in custody and was taken to a hospital.

Five people were wounded during the shooting at LAX, including the alleged gunman. One person, 39-year-old Transportation Security Administration officer Gerardo I. Hernandez, was killed. Hernandez was the first TSA officer in the agency’s 12-year history killed on the job, according to The Associated Press. "No words can explain the horror that we experienced today," TSA Administrator John Pistole said Friday in a message to employees.

The shooting at LAX resulted in flight delays all over the country. U.S. aviation officials stopped planes bound for LAX from taking off from other airports. Other LAX-bound flights already in the air were diverted to other airports.

At Los Angeles International Airport, arriving travelers were stopped several miles from the terminals for hours. Thousands of people lined the streets later, many wheeling suitcases, as the airport slowly reopened later in the afternoon.

According to CBS, 23-year-old Paul Anthony Ciancia lives in Los Angeles, but graduated high school from an all-boys Roman Catholic school in Wilmington, Del., in 2008. His family lives in Pennsville, N.J. According to Associated Press, Ciancia’s father owns an auto-body shop in southern New Jersey.

CBS Philly reported that Ciancia’s family told Pennsville police they had no reason to believe their son was mentally ill. They also said that the last time they saw their son, who moved to Los Angeles a year and a half ago, was over the summer when he visited his family to attend a wedding. “They are upset. This is a shock to them. This is a shock to our community,” Pennsville Township Police Chief Allen Cummings told CBS. Neighbors said Ciancia was a friendly and nice kid.

A former roommate of Ciancia told reporters there were no red flags indicating that the alleged gunman was disturbed. "He said he was going back to Jersey, going to work for his dad, and making amends with family problems ... and spending holidays with his family," James Mincey, Ciancia’s former roommate in Los Angeles, told KABC-TV.

Marc Kreiner, owner of a restaurant called The Morrison in Los Angeles where Ciancia frequented, told the Los Angeles Times that Ciancia was “kind of a quiet guy” who came in to the restaurant alone. 

According to KTLA, in the days leading up to Friday’s LAX shooting, Ciancia sent a series of “angry, rambling” text messages to family members, including one to Ciancia’s younger brother that made Ciancia’s father think his son was suicidal.

“Their younger child got a text message from Paul stating that there were some comments in there about his well-being and he wanted to possibly take his own life,” Chief Allen Cummings told reporters. Ciancia was apparently disgruntled about the Transportation Security Administration, saying in a note that they had violated his constitutional rights. He apparently referred to himself as a “pissed-off patriot.”

According to HLNTV, Ciancia had material on him that expressed anti-government and anti-TSA sentiment. He also may have been a believer in The New World Order, generally considered a conspiracy theory in which a group of elites are thought to be forming a one-world government.

Police are still trying to finger what exactly set Ciancia off and led him to attack TSA employees at LAX on Friday.