The brother of the man behind the San Bernardino terror attack and two Russian sisters have been charged with marriage fraud in a case that was unrelated to the December shootings but came to light in the investigation that followed it.

The accused include Syed Raheel Farook. His brother and sister-in-law, Syed Rizwan Farook and Tashfeen Malik, died in a shootout with police after killing 14 people and wounding 22 others on Dec. 2.

Also arrested Thursday were Syed Raheel Farook's wife, Tatiana, and her sister, Mariya Chernykh. Prosecutors say Mariya's marriage to Enrique Marquez Jr., the only person charged in the shootings, was a sham designed to enable her to obtain legal status in the U.S. after overstaying a visitor visa in 2009.

Marquez confessed to the scheme when authorities questioned him about the shootings, and he acknowledged getting $200 a month to marry Chernykh, according to his criminal complaint.

The three each entered not guilty pleas at an arraignment late Thursday afternoon in federal court in Riverside. They were ordered to stand trial June 21 in federal court in Los Angeles. Federal Judge David Bristow also scheduled a pretrial conference for June 6 in Los Angeles.

Bristow ordered that Chernykh, who prosecutors allege was most culpable for the sham marriage, be subject to electronic monitoring. Her boyfriend, who is the father of her child, arrived in court late Thursday afternoon to tell the judge he would post her $50,000 bond.

The mother of the Farook brothers posted bonds of $25,000 each for her oldest son and his wife. Her son left court shortly thereafter, declining to speak to reporters. His wife was expected to be released later in the evening.

Farook, who like the others appeared in court with shackles on his hands and feet, wept at times during his arraignment and bail hearing, including when his mother came forward to tell the judge she was posting bail.

"This is about a misrepresentation of an act of marriage. This is not about terrorism," his attorney, Ronald Cordova, told Bristow as he argued for a reasonable bail, maintaining that Farook is not a flight risk or a danger to society.

Outside court he said Farook has cooperated with federal authorities throughout the terrorist investigation.

"I think his thorough cooperation may have led to some of the trouble he's going through now," Cordova said, adding that in discussing his family situation forthrightly Farook never stopped to consider that he might be involved in any illegal activity regarding his sister-in-law's marriage.

If convicted of conspiracy to make false statements on federal immigration documents, the Farooks and Chernykh face up to five years in prison. Chernykh also is charged with fraud, misuse of visas and other documents, perjury and two counts of making false statements, which could mean up to 25 years in prison.

The government may have brought the charges as a bargaining chip in order to get more information that the Farooks and Chernykh haven't shared, said James Wedick, a former FBI agent who was with the agency 35 years.

"It suggests to me they weren't talking so the government decided to ask a grand jury to return charges," Wedick said. "If they were cooperating, they'd probably make some kind of deal."

While the government can benefit from continued interviews with the trio, Wedick said they also stand to benefit.

"It's a mechanism for both the government and the defense lawyers to use to better their position — with the government trying to get information relative to terrorism, and the defense looking to resolve the matter without prison time," he said.

According to an indictment unsealed Thursday, Syed Raheel and Tatiana Farook participated in the sham by acting as witnesses to the union of her sister and Marquez, and by creating a joint checking account along with a backdated lease to make it appear as if all four of them lived together.

Tatiana Farook also accompanied her sister to buy a $50 wedding ring, and Marquez and Chernykh posed in photographs that were staged to make the marriage appear real, prosecutors said.

All the while, Marquez was living with his mother next door to the house where the Farook brothers grew up, and Chernykh was living in a different city with her boyfriend, according to the criminal complaint against Marquez.

The FBI has not ruled out that someone other than the dead couple knew about or helped plan the attack.

"Those questions are still lingering," Eimiller said. "Did they have help? Did they have some support of any form? This is very much a continuing investigation and will be for some time."

Syed Rizwan Farook's family maintains they had no inkling about the plot. His mother, Rafia Farook, lived with him, Tashfeen Malik, and their newborn daughter in a townhome near San Bernardino. She said she never saw anything to suggest her son and daughter-in-law were planning a massacre.

Malik was from Pakistan and came to the U.S. in July 2014 so she could marry Rizwan Farook, whose parents were born in Pakistan. Farook was born in Chicago and grew up in Southern California.

___

Follow Amanda Lee Myers on Twitter at https://twitter.com/AmandaLeeAP. Her work can be found at http://bigstory.ap.org/content/amanda-lee-myers.