Authorities are trying to figure out why a gunman took an assault rifle into Los Angeles International Airport's Terminal 3 on Friday and opened fire on Transport Security Agency officials, killing one and injuring a handful of others. 

The shooter, identified by police as 23-year-old Paul Anthony Ciancia, took out an AR-15 assault rifle shortly after 9 a.m. Friday and fired his way through the airport, aiming at TSA officials the entire time. Gerardo I. Hernandez, 39, a father of two, was the first TSA officer killed in the line of duty in the organization's twelve year history. 

Ciancia was eventually subdued after a short gunfight with an airport police officer and sergeant. "They hit him multiple times before he went down," a law enforcement source told the L.A. Times. He was allegedly shot in the head and leg, making it difficult for authorities to question him about his deadly attack. Ciancia is still in critical condition at UCLA Medical Center. 

While authorities wait for Ciancia to heal, the investigation into his behavior that might reveal a motive for yesterday's shooting continues. According to multiple reports, a handwritten note was found in the bag the suspected gunman brought to the airport expressing "disappointment in the government" and a desire to not hurt "innocent people." Most suspect he had no plans to leave the airport alive. "This was clearly a suicide mission... he did not expect to walk away from this," a federal official told USA Today.

John Mincey told KABC-TV the two men lived together until February, but they stayed in contact and had lunch together just last week. "I'm absolutely shocked," Mincey told the ABC affiliate. "I'm still trying to wrap my brain around it because from knowing this guy, it just doesn't make sense." Mincey said Ciancia never behaved suspiciously or made any hateful or prejudice remarks while they lived together. As far as he knew, Ciancia was heading back to his hometown in New Jersey to be with family over the holidays. "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. That's all I know," Mincey said.