SAN BERNARDINO >> Enrique Marquez checked himself into a mental health facility in Long Beach under a psych hold soon after two radicalized terrorists gunned down 35 San Bernardino County employees at a Christmas Party killing 14.

Marquez, 29, was released from the unnamed facility Sunday, and sources close to the investigation from within the FBI told this newspaper that they’re continuing to question him about his role in supplying weapons to Syed Farook and Tashfeen Malik, the perpetrators of Wednesday’s massacre.

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In addition to providing information about the rifles, Marquez may have other information that could help federal investigators as they continue to probe the shooter’s background, NBC National News reported.

Farook and Malik planned their actions in advance and engaged in target practice in Los Angeles days before the deadly shootings, FBI Assistant Director David Bowdich said Monday.

“This investigation is massive in scale,” Bowdich said during a news conference outside the San Bernardino Police Department, adding that the FBI’s Joint Terrorism Task Force worked through the weekend gathering additional evidence.

“As the investigation has progressed, we have learned that both subjects were radicalized and had been for some time,” Bowdich said.

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Bowdich declined to discuss Marquez, Farook’s former Riverside neighbor and childhood friend, whose home was searched by federal agents Saturday.

All the guns used in the shootings were purchased legally in California, between 2007 and 2012, said John D’Angelo, assistant special agent in charge with the Bureau of Alcohol, Tobacco and Firearms.

Farook had purchased two handguns and a 22-caliber rifle and Marquez two assault rifles. Investigators are trying to determine how the assault rifles got from Marquez to Farook, D’Angelo said.

Both rifles were purchased three years ago, the FBI sources said.

While both rifles when purchased were legal to possess in California, with magazine locking devices known as bullet buttons, the weapons were eventually altered to make them more effective, said Meredith Davis, special agent with the ATF.

One of the rifles, the Smith & Wesson M&P15, was converted to fire in fully automatic mode, and the DPMS Model A-15 was modified to take large-capacity magazines, she said.