SALT LAKE CITY — Two Salt Lake City biodiesel executives linked to a polygamous group will stay in jail after prosecutors argued they could flee to Turkey if released ahead of trial in an alleged $511 million tax credit scheme.

The men have access private jets, millions of dollars stashed abroad and an unidentified federal law-enforcement contact who apparently tipped them off ahead of a raid, special assistant U.S. Attorney Leslie Goemaat said at a hearing on Wednesday.

"There are very real safety concerns for witnesses in this case," she said.

Washakie Renewable Energy CFO Isaiah Kingston's attorney said the prosecutor's allegations are false hearsay.

"He does not have any access to private jet. He has been on one once that had nothing to do with this case," said Scott Williams. "If anyone made an allegations against you based sorts of things they brought up, you would be appalled."

U.S. Magistrate Judge Brooke Wells refused an effort to immediately release Kingston, though he's due back in court on Friday.

A lawyer for his brother, company CEO Jacob Kingston, asked for a detention hearing next week so he can secure defense attorneys from Washington, D.C.

The men are charged with creating fake production records to get renewable-fuel tax credits from 2010 to 2016, then laundering the proceeds. The company once described itself as the largest producer of clean burning and sustainable biodiesel in the state.

Prosecutors said both men are members of the northern Utah-based Davis County Cooperative Society, also known as the Kingston Group, which practices polygamy and owns hundreds of businesses. Investigators said in court documents members have previously hidden people wanted by police.

A spokesman for the group, Kent Johnson, said in a statement that leaders strongly condemn fraudulent business practices, though members make their own decisions. The group also encouraged "all parties to comply with lawful orders of the court."

Federal agents raided offices and homes associated with Washakie Energy during their investigation in February 2016. They said they found computers had been recently wiped, that desks were empty and bookcases contained dust outlines where binders of documents had been stored.

It's not clear how executives allegedly knew about the sealed search warrants, but investigators have said Jacob Kingston told a witness he was tipped off by a federal agent. Investigators from the Environmental Protection Agency, the Internal Revenue Service and the Defense Criminal Investigative Service are among those that have worked on the case.

Meanwhile, Washakie has invested at least $130 million in Turkey, and the brothers own a home there, according to court documents. Jacob Kingston was arrested last week at the Salt Lake City airport with his wife and some of his children as they were about to travel to Turkey, prosecutors said.

Their co-defendant, California businessman Lev Aslan Dermen, has a private plane and previously flew to Turkey when investigators served search warrants on his home in a separate case, prosecutors said. No attorney was listed for him in court records, and he did not appear in the Utah courtroom on Wednesday.

If convicted of charges that include filing a false tax return and money laundering, Jacob Kingston faces up to 87 years in prison. Isaiah Kingston faces up to 20 years.