(CNN) -- The family of Army Sgt. Bowe Bergdahl have received threats following his release after five years in captivity at the hands of the Taliban, an FBI spokesman told CNN on Saturday.
"We are working jointly with our state and local partners and taking each threat seriously," FBI Special Agent William Facer said in an e-mail.
Facer declined to detail the nature and severity of the threats.
A fallen soldier's mother and a former member of Army Sgt. Bowe Bergdahl's unit pressed assertions Saturday that troops were killed while searching for him in Afghanistan. Officials say that there is no such evidence.
"Yes, men were injured and killed in the search for him," former Sgt. Matt Vierkant, a member of Bergdahl's platoon, told CNN. "The mission was to find Bergdahl."
Pentagon and Army officials have looked at such claims, and "right now there is no evidence to back that up," a U.S. official told CNN on Thursday.
Bergdahl went missing in Afghanistan in June 2009 and was captured by the Taliban, which released him a week ago, after almost five years' captivity, in exchange for five Taliban prisoners held at Guantanamo Bay.
Also making claims of troop deaths in the Bergdahl search was Sondra Andrews, the mother of 2nd Lt. Darryn Andrews, who was killed in September 2009.
Andrews said she believes that her son and other troops "were strictly on a mission looking for Bergdahl," she told CNN on Saturday.
That information is "based on the men that served with Darryn," she said.
Andrews said that military should give her family information "on what Darryn was doing and why they lied to us."
She endorsed accusations by former unit members that Bergdahl deserted and caused U.S. troops to die in the search for him -- though Defense Secretary Chuck Hagel said it's "unfair" to Bergdahl and his family to presume anything about his disappearance.
"I'd like to see Bergdahl given an opportunity to tell his story, be on trial, have the witnesses come forward and tell their story and get the truth through that, and then I would like to see the full measure of the law followed for his punishment," Andrews said.
The six soldiers at the center of the Bergdahl debate
The Army has no definitive finding that Bergdahl deserted because that would require knowing his intent -- something Army officials couldn't learn without talking to the soldier, a U.S. military official told CNN.
An Army fact-finding investigation conducted in the months after his disappearance concluded that Bergdahl left his outpost deliberately and of his own free will, according to the official, who was briefed on the report.
Secretary of the Army John McHugh said this week that the military will conduct "a comprehensive, coordinated" review of Bergdahl's case, including "speaking with Sergeant Bergdahl to better learn from him the circumstances regarding his disappearance and captivity."
In the week since Bergdahl was released by the Taliban, a controversy has grown over whether troops were killed, directly or indirectly, in the search.
Susan Rice defends Bergdahl comments, calls his service 'honorable'
Former soldiers involved in the operations asserted to CNN this week that at least six soldiers were killed in the search for Bergdahl.
Also this week, Nathan Bradley Bethea, a former member of Bergdahl's battalion who searched for him that summer in 2009, wrote in the Daily Beast that eight soldiers' deaths were tied to the Bergdahl search. Bethea provided the eight soldiers' names -- including six names that CNN earlier reported.
New York Times reporter Andrew W. Lehren co-wrote an article this week stating that "a review of casualty reports and contemporaneous military logs from the Afghanistan war shows that the facts surrounding the eight deaths are far murkier than definitive."
Lehren told CNN on Saturday, however, that he wasn't dismissing the accounts advanced by relatives of killed soldiers and former members of Bergdahl's unit.
"I don't think we're disputing what these people are saying," Lehren told CNN's Michael Smerconish. "We're just saying that the military, itself, in their own words, written at the time before all of this other freight is being brought onboard, the military in its own words is painting a more complicated story."