San Bernardino - Just days before he carried out an attack that killed 14 people, Syed Farook practised with a rifle during one of several recent visits to a local shooting range, authorities said. Sometimes he was joined by his wife, his partner in the carnage.
An instructor at Riverside Magnum Range - about 30km from the Inland Regional Centre where the two targeted Farook's co-workers a few days later - said Farook visited the range on November 29 and 30.
John Galletta said on Monday that nothing was out of the ordinary about Farook's behaviour, but that he asked a representative why his rifle might be smoking, and was told it was most likely because it was new.
Asked whether in hindsight he or others at the range should have been suspicious of Farook, Galletta said: "How are you able to determine what somebody's intents are?"
As more details on the married couple emerged, the FBI said Farook and Tashfeen Malik had long since embraced radical ideology.
"We have learned and believe that both subjects were radicalised and have been for quite some time," David Bowdich, chief of the FBI's Los Angeles office, said at a news conference on Monday.
He added: "The question we're trying to get at is how did that happen and by whom and where did that happen? And I will tell you right now we don't know those answers."
Authorities also disclosed that a year before the rampage, Syed Farook's co-workers at the county health department underwent "active shooter" training in the same conference room where he and his wife opened fire on them last week.
It was not immediately clear whether Farook attended the late-2014 session on what to do when a gunman invades the workplace, San Bernardino County spokesperson Felisa Cardona said.
Two employees who survived the attack said colleagues reacted on Wednesday by trying to do as they had been trained - dropping under the tables and staying quiet so as not to attract attention.
"Unfortunately, the room just didn't provide a whole lot of protection," said Corwin Porter, assistant county health director.
Farook, a 28-year-old restaurant inspector born in the US to a Pakistani family, and Tashfeen Malik, a 29-year-old immigrant from Pakistan, went on the rampage at a holiday luncheon at about the same time Malik pledged allegiance to the Islamic State group on Facebook, authorities said. The two were killed hours later in a gun-battle with police.
Authorities also discovered 19 pipes in the couple's home in Redlands, California, that could be turned into bombs, Bowdich said. The FBI previously said it had found 12 pipe bombs.
Newly released emergency radio transmissions from the fast-moving tragedy show that police identified Farook as a suspect almost immediately, even though witnesses reported that the attackers wore black ski masks.
An unidentified police officer put out Farook's name because Farook had left the luncheon "out of the blue" 20 minutes before the shooting, "seemed nervous," and matched the description of one of the attackers, according to audio recordings posted by The Press-Enterprise newspaper of Riverside.
In addition to the 14 killed, 21 people were hurt. At least six remained hospitalised, two in critical condition.