The government's case was weakened when prosecutors said a key witness, a Somali refugee and former gang member, repeatedly refused to testify, saying he is afraid for himself and for his family.
So prosecutors charged Abdullahi Farah with two counts of contempt of court and obstruction of a child sex trafficking case. He was convicted by a jury in April.
Farah, 24, said he was attacked and pistol whipped when word got out that he was cooperating.
"What choice do I have?" he said during a jailhouse interview with The Associated Press. "If I testify, they will either kill me or kill my family."
Farah is facing a maximum of 20 years in prison for the obstruction conviction. There is no mandatory maximum sentence for contempt and a prosecutor has said Farah will face up to life in prison when he is sentenced at a date yet to be determined.
Legal experts say the case is extraordinary because it's almost unheard of for prosecutors to come down so hard on one of their own witnesses, and for the reluctant ones to face so much prison time for not cooperating.
"This is exceedingly rare," said Nancy Hoppock, the director of a criminal law center at New York University Law School who spent 19 years as a state and federal prosecutor. She said prosecutors may have felt like they were left with no other choice.
The big unanswered question is how much Farah's testimony would have helped the government.
Assistant U.S. Attorney Van Vincent, the lead prosecutor, declined to discuss Farah, saying it would not be appropriate before sentencing. For his part, Farah said he knows nothing about the child sex trafficking and only helped prosecutors identify gang members by listening to hours of secretly recorded conversations of defendants talking to one another.
Court documents and transcripts of Farah's trial said he admitted to having information material to the case, but the paperwork doesn't spell out what the information is.
Former U.S. Attorney Ed Yarbrough, the top federal prosecutor in Nashville when the alleged Somali gang members were indicted in November 2010, said witnesses will generally start cooperating after being threatened with jail or locked up on a material witness warrant.
"It almost never comes to this," Yarbrough said.
Federal agents testified Farah never told them he was attacked until after he fled to Louisiana to avoid testifying, according to court documents. Agents said Farah gave conflicting accounts and sketchy details about both attacks, and U.S. District Judge Todd Campbell also said he had problems with Farah's credibility.
Farah spent two years helping prosecutors before he decided to stop talking, court records show.
Farah, who has lived in Nashville and Minneapolis, said he gave up the gang to redeem himself in his family's eyes, and he insisted members were engaged in burglary and using drugs, not sex trafficking, when he was involved.
Those accused in the sex trafficking ring are alleged to be gang members who sold girls in Minnesota, Ohio and Tennessee.
Farah has convictions for commercial burglary and lost his legal right to be in the U.S. He said he agreed to cooperate with authorities to help him with his immigration status.
Farah said he was told he'd probably never have to testify because the defendants would probably plead guilty. So far, only one defendant pleaded guilty to a charge of making false statements. The sex trafficking charges against that defendant were dismissed.
Nine defendants went to trial last year. A jury acquitted six and found three guilty. A federal judge later tossed out those convictions, saying prosecutors failed to show that they were part of one overarching conspiracy.
Farah said word got out that he was helping authorities, and he was told gang members were coming for him. He said a group of men surrounded him in August 2011 just outside his Nashville home and beat him and pistol whipped him in the first of two attacks. Instead of telling federal agents, he fled to Louisiana.
He was brought back to Nashville and jailed, then released with an ankle monitor.
After refusing to testify, Farah was put back behind bars for four months and ordered to give a deposition that would be used when the remaining defendants in the sex trafficking case are tried. Again, he refused to talk. He was indicted and went to trial in April.
Early on, Farah didn't have an attorney. Now, he is appealing his contempt and obstruction convictions.
"The best advice that I can give to anyone asked to provide information in a criminal investigating is to first consult with an attorney and to get any agreements with the government memorialized in writing," said Farah's attorney, James Mackler.