FBI Handout Gunman who killed a security agent at LAX was carrying a note expressing 'disappointment in the government', reports claim.

In pictures: Shooting at Los Angeles Airport

The gunman who opened fire inside Los Angeles International Airport, killing a security agent and injuring several others, was carrying a note describing himself as a "pissed off patriot" who wanted to shoot "pigs", it has been reported.

In the hours after Friday's deadly attack, suggestions began to emerge that the shooter - identified as Paul Ciancia, 23 - was motivated by extremist anti-government views as well as emotional problems that had pushed him towards thoughts of suicide.

Authorities have declined to address his motivation publicly but a law enforcement official told the Los Angeles Times that a note was found on Ciancia expressing "disappointment in the government" and claiming he had no interest in harming "innocent people".

Instead, he wanted to "kill TSA", the note reportedly stated, a reference to the Transport Security Administration created in the wake of the September 11 attacks to increase safety on US transportation. The written rant was said to detail Ciancia's belief that his constitutional rights were being violated by TSA searches and his anger at former Department of Homleand Security Secretary Janet Napolitano.

As he embarked on his shooting spree, dressed in fatigues and carrying a high-powered rifle, Ciancia asked several cowering members of the public if they were TSA, witnesses claimed. He found his target, shooting dead 39-year-old agent Gerardo Hernandez, the first TSA officer to be killed in the line of duty since the agency's creation.

A number of other agents suffered gunshot wounds.

The deadly attack threw one of the world's busiest airports into chaos as terrified passengers fled Terminal 3, some gathering on the airside tarmac under the wings of waiting planes. Others locked themselves in bathrooms as security officers sought to fell the shooter, ultimately engaging him in gunfire which resulted in shots to his mouth and leg, and taking him into custody.

Ciancia, originally from New Jersey, reportedly began his assault at a check-in counter where he pulled an assault rifle out of a bag and opened fire. Witnesses heard several "popping" sounds before the gunman moved up an escalator, and through a security screening area to where passengers were waiting for their flights outside boarding gates.

He was then shot and wounded by police, reportedly near a Burger King stand. Up to a dozen shots were heard by passengers as they scrambled away.

Ciancia had at least five full 30-round magazines with him, police said. He was shot in the mouth and leg by two airport police officers.

Ciancia had earlier that day sent a text message to his brother saying that he intended to take his own life. This led his father to contact police in the family's home state of New Jersey expressing concern for his state of mind and asking for help in locating him. They in turn contacted police in Los Angeles who sent a patrol car to Ciancia's apartment in the city. There, his two roommates said they had seen him the previous day and that he appeared to be fine.

A former classmate of Ciancia's told the LA Times that the suspected shooter was a loner and suffered bullying at their private school.

"In four years, I never heard a word out of his mouth," said David Hamilton, who graduated with Ciancia from Salesianum School in Wilmington, Delaware, in 2008. "He kept to himself and ate lunch alone a lot. I really don't remember any one person who was close to him."

Witnesses said Ciancia appeared calm and composed as he picked his way through the terminal seeking targets. But passengers, who included a number of TV and film celebrities, told of their terror during the ordeal.

Emmy-nominated actor Tim Daly, who appeared in The Sopranos, was in the Virgin first class lounge on the other side of a wall from the shooting.

"Less than a minute after the shots the LAPD burst into the lounge with weapons drawn to make sure there were no bad guys in the lounge," he said. "That was pretty frightening."

Daly said when he was evacuated he saw a gun that looked like an AR-15 assault rifle with three clips on the floor outside Gates 35 and 36.

He said: "It was right in the middle of where everyone waits to get on their planes. We were told not to step on any blood or bags because it was evidence."

TV presenter Tory Belleci, from the show Mythbusters, tweeted:

Twitter: Tory Belleci - Heard gun shots then everyone starting running for the door. Not sure if anyone was hurt. #LAX

The airport, known as LAX, serves about 64 million people a year, with more than 1,500 flights taking off and landing every day. Terminal 3 is home to Virgin America and other airlines. All flights were grounded and President Barack Obama was being kept informed.

Passenger Sarah Richardson said: "We heard a lot of loud gunshots. My colleague threw me to the ground and we were scrambling. Somebody told us to make a run for it. We got into a room and they pulled a coffee machine in front of the door. We could hear gunshots outside.

"The sound was so loud we thought a bomb had gone off. Some people hid in a bathroom. It was pure and utter mayhem, people tripping over each other crying and screaming, bags everywhere."

Eyewitness Brian Adamick, 43, told the Los Angeles Times he saw a wounded TSA agent with a bloody leg on the tarmac.

"It looked like it was straight out of the movies," he said. The agent told him "I got shot, I'm fine," adding that he had been shot before.

Los Angeles chef Vernon Cardenas, who was en route to Philadelphia to audition for the MasterChef TV programme, said the gunman looked at him but didn't shoot.

He described a white man in his 20s with "dirty blonde hair". Mr Cardenas said: "He was dressed in navy blue clothes, he almost looked like an employee of the airport. He was walking around in sort of a daze."

The television channel AMC confirmed that scenes for its award-winning drama Mad Men were being filmed at the airport at the time of the shooting.

Production on Mad Men was taking place at nearby Terminal 4 and a member of the crew said on Twitter: "We are filming at LAX. Gun fire. Locked down. Evacuating. Terminal 4. Forced back inside for safety."

It was not clear which members of the cast were present at the airport at the time.

Mythbusters presenter Tory Belleci told CNN: "People were running towards me screaming 'There's a shooter, there's a shooter.' I heard the shots. Everybody was jumping over each other and trying to stay low. It was blowing my mind how he could get a weapon that far into the airport."

Fellow Mythbusters star Grant Imahara said: "To be there was surreal and you went into survival mode. It was like the whole airport was holding its breath for an hour."

Passenger Leon Saryan, who was walking from the security check carrying his shoes and belt, told ABC News: "I was cowering in a corner. He (the gunman) looked at me and he said, 'TSA?' I shook my head no, and he kept on going. I just prayed to God. That's all I did. I just prayed."