NEW YORK (NYTIMES) - A man who supplied the weapons that were used by a couple to kill 14 people in San Bernardino, California, in 2015 was sentenced on Friday (Oct 23) to 20 years in federal prison.

The man, Enrique Marquez Jr, 28, pleaded guilty in 2017 to providing the two assault rifles that were used by his friend, Syed Rizwan Farook, and Farook's wife, Tashfeen Malik, in the attack at a holiday party on Dec 2, 2015, with Farook's co-workers at a social services centre. Marquez also pleaded guilty to plotting two unrealised terrorist attacks in California in 2011 and 2012.

In pleading guilty, Marquez had acknowledged making false statements in connection with his role as a "straw buyer" of the rifles, federal prosecutors said.

Farook and Malik were killed in a shoot-out with the authorities hours after the massacre, which was the worst terrorist attack on American soil since Sept. 11, 2001, federal prosecutors said. Marquez, of Riverside, California, did not participate in the shooting, which also injured more than 20 people.

The authorities have called the shooting an ISIS-inspired attack and have pointed out that Malik pledged allegiance to the Islamic State in Iraq and Syria on Facebook on the day of the shooting.

Federal prosecutors said Marquez had admitted in a plea agreement and in open court that he had also plotted with Farook in 2011 and 2012 to attack Riverside City College and a California freeway.

Those attacks were never carried out, but Marquez had discussed with Farook using radio-controlled improvised explosive devices for the attacks and bought Christmas tree light bulbs and a container of smokeless powder to use in the devices, federal prosecutors said.

In court on Friday, relatives of the victims asked Judge Jesus Bernal of US District Court in Central California to impose a lengthy sentence.

"He's a terrorist, your honour," said Mr Gregory Clayborn, whose daughter, Sierra, was killed, The Associated Press reported. "And if you let him out, he's going to do it again."

In imposing a 20-year sentence, Judge Bernal denied a request by Marquez's lawyer for a five-year sentence, which prosecutors said would essentially have been equal to time served and would have resulted in Marquez's swift release from custody.

Federal prosecutors called Marquez's request an attempt to "downplay the seriousness of his actions and skirt that his actions contributed to the mass killing". He had faced a maximum sentence of 25 years in prison.

"This defendant was an active member of a conspiracy that planned to inflict death and destruction on innocent people," first assistant US attorney Tracy Wilkison said in a statement on Friday. "Today's sentence is the direct result of actions that enabled a terrorist and laid the foundation for an attack that took 14 innocent lives, wounded 22 others and shook the entire nation."

Marquez's lawyer, Mr John Aquilina, said in a phone interview that his client had spent seven years in a "subservient role" to Farook. He said Marquez was 13 when he met Farook, who was 18 and was his neighbor in Riverside in 2005. He said Marquez essentially left his own family to be with Farook.

"He was attracted to the Farook family and felt part of the family he didn't have at home," Mr Aquilina said. "That's pretty much why Marquez was in a subservient role, following Farook wherever he went and doing whatever he did."

He said Farook had persuaded Marquez, who was raised Roman Catholic, to convert to Islam when he was 16.

"It just shows you the domination that Farook had over Marquez," Mr Aquilina said. "By all accounts, it was Farook who was the mover and shaker." Marquez eventually cut off contact with Farook in 2012 after Farook assaulted him, Mr Aquilina said.

Soon after the attack in San Bernardino, investigators uncovered evidence that Marquez in 2011 and 2012 bought the two rifles used in the shooting, federal prosecutors said. Marquez admitted in his plea agreement that Farook had paid him for the weapons, federal prosecutors said.

Marquez was arrested about two weeks after the massacre and has been in custody since his first court appearance, on Dec 17, 2015.