U.S. Attorney Andy Luger suggested on Friday that an accused jihadi sympathizer being held in nearly round-the-clock solitary confinement while awaiting trial may have tried to intimidate another defendant in the case who turned state’s witness.

Guled Omar, 21, who has been shuttled between several area jails since his arrest last April on federal charges of conspiring with others to join the Islamic State in Iraq and the Levant (ISIL), repeatedly tried to contact another defendant, Abdullahi Yusuf, while the two were in the Anoka County jail together, according to court documents filed Friday.

Yusuf pleaded guilty to conspiracy in February and agreed to testify against his friends as part of a government plea agreement.

Authorities didn’t elaborate on the nature of the alleged communications, which prompted Omar’s transfer to the Ramsey County jail.

“While Omar has denied the allegations that he has tried to intimidate or harass a cooperating witness, it was deemed prudent to have the two separated, which has been the case ever since,” Luger wrote in the letter, addressed to U.S. District Judge Michael Davis. “To my knowledge, we have received no reports that other defendants have tried to contact Yusuf, and no other defendants have been moved for this reason.”

Last week, the U.S. Marshals Service, which oversees Omar’s detainment, said that he was placed in “administrative segregation” for his own protection 23 hours a day, at the FBI’s behest.

Omar’s family spoke out last week after being repeatedly turned away while trying to visit him in jail. His mother, Fadumo Hussein, said her son was living under “inhumane” conditions at the jail.

In the letter, filed Friday afternoon in federal court, Luger contested the family’s charge, saying that he takes such allegations seriously.

In one of several recorded jail conversations, Luger wrote, Guled is heard laughing and telling the person on the other line that he was “enjoying his time.”

The letter drew an angry response from the defense.

“I have a hard time believing that the U.S. attorney is so tone deaf that he can’t understand the sarcastic tenor of his comment,” Omar’s attorney Glenn Bruder said by phone Friday.

Bruder, who said that he hadn’t heard the recordings, declined to comment further on the matter.

FBI spokesman Kyle Loven on Friday referred questions to the U.S. attorney’s office, which declined to comment beyond the letter.

Prosecutors allege that Omar, who was attending community college and working as a security guard at the time of his arrest, was part of a year-old conspiracy of at least a dozen men who sought to aid ISIL.

Federal authorities this week filed a broader indictment, which brought additional charges against some or all of the defendants, including conspiracy to commit murder abroad, which carries a maximum sentence of life in prison.

Several defense attorneys and families of the remaining defendants said the new indictment was part of a thinly veiled effort by federal prosecutors to pressure the men into pleading guilty.

Authorities are still determining whether additional charges will be brought.