Federal authorities are preparing criminal charges against a man who investigators say supplied guns to the married couple who killed 14 people at a disability centre Christmas party in California, this month, government sources say.
Enrique Marquez, a friend and former neighbour of radicalised Muslim Syed Rizwan Farook, 28, and his wife, Tashfeen Malik, 29, the couple who carried out the December 2 San Bernardino attack could be charged as early as Thursday (local time), CNN and NBC reported, citing unnamed law enforcement officials.
US prosecutors were considering filing firearms charges against Mr Marquez, with state gun charges also possible, one of the government sources said on the condition of anonymity.
Mr Marquez, 24, who had checked himself into a Los Angeles-area psychiatric facility shortly after the shootings, had several connections to Farook and Malik and quickly became a key figure in the investigation of the shootings.
The Federal Bureau of Investigation, which is treating the attack as an “act of terror”, raided his home and questioned him for several days. Sources said Mr Marquez cooperated during their interviews.
During the investigation, a law enforcement source said Marquez, who had converted to Islam, and Farook apparently had plotted some sort of attack around 2012 but abandoned the idea.
Mr Marquez, who had known Farook since they were teenage neighbours in the city of Riverside, legally purchased the two AR-15 assault-style rifles that the couple used in their attack on a holiday party of Farook’s co-workers.
Farook, the US-born son of Pakistani immigrants, and Pakistani-born Malik were killed in a shootout with police a few hours after their assault on the party.
Marquez and Farook were close childhood friends
Mr Marquez, who had worked at Walmart and at a bar recently, also is related to Farook’s family by marriage.
In 2014, according to state records, Mr Marquez married a Russian woman who was the sister of Farook’s older brother’s wife. Neighbours said they were surprised to learn that he had been married, having never seen him with a woman.
The FBI said Farook and Malik had discussed martyrdom online before they even met and were supporters of IS, the violent group that has taken over large parts of Syria and Iraq.
Their attack, which left 21 people wounded, has stirred concerns among Americans about national security and the reach of IS becoming an issue in the US presidential campaign.
The attack came a few weeks after gunmen and suicide bombers affiliated with Islamic State (IS) killed 130 people in a series of co-ordinated attacks in Paris.
FBI Director James Comey on Wednesday said there was no evidence that the San Bernardino attackers, who were also inspired by IS had been part of a terrorist cell.
Neighbors said Mr Marquez and Farook often worked together on cars in Farook’s garage in their younger years but that the friendship had cooled in the past three years.
Mr Marquez converted to Islam about the time that Farook became more devoted to the faith around 2008.
But Azmi Hasan, manager at the Islamic Society of Corona-Norco, said Mr Marquez later told him that Islam was not for him.
President Barack Obama is due to travel to San Bernardino on Friday to meet privately with families of the San Bernardino victims.