The gunman who allegedly killed a security officer at Los Angeles airport carried a note saying he planned to murder "multiple" agents, prosecutors said as they announced charges against him.
A prosecutor told how Paul Ciancia allegedly opened fire at "point-blank range" on Gerardo Hernandez, the first Transportation Security Administration agent killed since the office was created following the September 11, 2001, terrorist attacks.
The dead officer's widow, meanwhile, said she was "truly devastated" by his death.
"He was a joyful person, always smiling and took pride in his duty to the American public," Ana Hernandez said.
Ciancia, who used a Smith & Wesson assault rifle and a large stock of ammunition in the attack, faces a possible death penalty on charges of murdering a federal officer and committing violence at an international airport.
The gun rampage on Friday triggered chaos at LA International Airport (LAX), disrupting more than 1500 flights. The airport only fully reopened more than 24 hours later.
Describing how the shooting started, a prosecutor said Ciancia pulled a ".223-calibre M and P-15 assault rifle out of his bag and fired multiple rounds at point-blank range" at Hernandez, 39.
The shots wounded the unarmed TSA officer but did not kill him. The 23-year-old gunman, dressed in black and wearing a bullet-proof vest, then went up a nearby escalator and came back down to "shoot the wounded officer again," US attorney Andre Birotte said.
Ciancia then proceeded further into the terminal, shooting four more people, including two other TSA officers, before being detained following a gunfight with airport police.
The alleged gunman, who remains in hospital and has not yet answered questions from investigators, carried a note in his bag indicating that "he targeted especially TSA officers," for whom he felt "anger and malice".
The handwritten note showed he "made a conscious decision to kill multiple TSA employees", said David Bowdich, the head of the FBI's Los Angeles office.
"In the note that was handwritten by the defendant, that was signed by the defendant, we found a statement where he made a conscious decision to kill multiple TSA employees," Bowdich said.
"He addressed them at one point in the letter, and stated that he wanted to 'instil fear into their traitorous (sic) minds'."
Los Angeles Mayor Eric Garcetti said Ciancia had a lot of ammunition when he was arrested.
During the shooting spree, which lasted less than 10 minutes, Ciancia approached a number of people cowering in the terminal and pointed his gun at them, asking if they "were TSA", according to the Los Angeles Times.
If they answered "no" he moved on, the Times reported, citing witnesses who said he cursed the TSA repeatedly.
While officials have not released details about the suspect's condition, the Times said he was hospitalised in a critical condition after being shot in the head and leg.The FBI said Ciancia was a Los Angeles resident who was originally from the eastern state of New Jersey.