The man accused of buying two assault rifles used in last month's deadly San Bernardino attack pleaded not guilty Wednesday in a Southern California courtroom to charges in a federal indictment accusing him of conspiring with one of the shooters.

Enrique Marquez Jr., 24, appeared in federal court in Riverside with his hands and feet shackled. He answered "not guilty" when asked to enter his plea to the five-count indictment charging him with conspiring to provide material support to terrorists.

A jury trial was scheduled for Feb. 23, but the date could be postponed -- a status hearing is set for Feb. 8 to discuss scheduling. Marquez could be sent to prison for as long as 50 years if he's convicted.

According to the FBI, during 10 days of interviews, Marquez revealed plots he and his neighbor, Syed Rizwan Farook, discussed but never carried out to slaughter students at a community college and murder motorists on a congested freeway.

The Dec. 30 indictment superseded charges he originally faced when arrested two weeks after the Dec. 2 shootings carried out by Farook and his wife, Tashfeen Malik, at a building where Farook's colleagues from the San Bernardino county health department were meeting.

The couple killed 14 people and wounded 22 others before they were shot to death hours later in a dramatic gun battle with police.

Authorities said Marquez was not involved in the killings, but that his failure to warn authorities about Farook and his purchase of the guns had deadly consequences.

Marquez and Farook were friends who grew up next door to each other in Riverside. Farook, 28, introduced Marquez to Islam as a teenager a decade ago and indoctrinated him in violent extremism, according to the FBI.

Marquez bought two rifles for Farook in 2011 and 2012 and the two planned to launch bomb and shooting attacks at Riverside City College, where they attended classes, and a notoriously gridlocked section of highway without exits.

Marquez faces two firearms violations for being the so-called straw buyer who purchased the guns in his name because Farook, who was born in the U.S. to Pakistani immigrants, "looked Middle Eastern," authorities said.

He also faces charges of marriage fraud and lying on immigration paperwork for wedding to Russian woman whose sister is married to Farook's brother.

The FBI said Marquez admitted he was paid $200 to marry the woman and he lied on immigration papers that he lived with her so she could stay in the U.S.

A lawyer for Marquez previously argued unsuccessfully that his client should be released on bond because he had willingly spoken with the FBI while he was not in custody and never fled.

Public defender Young Kim has since filed paperwork in court to prevent investigators from speaking with Marquez without his lawyer present.