The Northern Virginia man added this week to the FBI’s “Most Wanted Terrorists” list has relatives who were killed or captured by al-Shabab, and family members are skeptical that he would have tried to help the Somali group, an attorney for the man’s brother said Friday.

The attorney, Gadeir Abbas, said Liban Mohamed’s family “rejects the allegations” against him and noted that the family has something of a fraught relationship with federal authorities. Abbas represents Mohamed’s brother, Gulet Mohamed, in a civil suit against U.S. officials that is not related to the criminal charge against Liban Mohamed.

“Al-Shabab killed his uncle, imprisoned his cousins, inflicted trauma on their family extensively,” Abbas said. “And Gulet understands better than most that there’s good reason to be skeptical of the government’s allegations.”

Abbas said that the Mohamed brothers came with their family to the United States many years ago to escape strife in Somalia and that many of them still live in Northern Virginia. Gulet Mohamed, now 23, has an information technology job, Abbas said. Federal authorities have said that Liban Mohamed, a naturalized U.S. citizen, worked as a cabdriver.

Abbas said that Liban Mohamed disappeared without explanation in the summer of 2012 and that family members reached out to federal investigators through attorneys to see whether they might know his whereabouts. He said investigators claimed that they did not. He said, to his knowledge, the family has not had contact with Liban Mohamed since that summer.

Liban Haji Mohamed (Courtesy of FBI)

On Thursday, federal prosecutors in Virginia unsealed an arrest warrant, filed in February 2014, charging Liban Mohamed with providing material support and resources to a designated terrorist organization. At the same time, the FBI announced that it was offering a $50,000 reward for information leading to his arrest and conviction.

FBI officials have not detailed why they believe Liban Mohamed is an al-Shabab supporter. They have said only that they think he helped recruit for the terrorist group and, in July 2012, left to join the fight in Somalia. They also have said they consider Liban Mohamed particularly dangerous because he has weapons training and knowledge of Washington infrastructure.

The Mohamed family has long been on the FBI’s radar.

In 2010, Gulet Mohamed, then 19, was detained and allegedly tortured by authorities in Kuwait, and then questioned by FBI agents, after his inclusion on a no-fly list kept him from traveling home to the United States.

According to an affidavit he submitted to the court, Liban Mohamed called and e-mailed authorities for days, begging for information about his brother’s whereabouts. He eventually received a call from Gulet Mohamed, who described being blindfolded, beaten and told to forget his family, according to the affidavit.

Gulet Mohamed was ultimately allowed to return to the United States and was not charged with a crime. He is suing over his inclusion on the no-fly list. On Friday, a federal judge in Alexandria heard arguments about whether the process used to put people on the list is unconstitutional.

The judge, Anthony J. Trenga, did not rule on the matter but asked pointed questions about the no-fly list. He asked a government attorney, for instance, whether there was any other program in all of U.S. history that deprived people of their liberty with so little transparency.

Abbas said it seemed curious that the government unsealed Liban Mohamed’s arrest warrant — and announced his inclusion on the list of most-wanted terrorists — a day before the hearing. “The timing is what I question the most,” he said.

A spokesman for the U.S. attorney’s office and an FBI spokeswoman declined to comment.