Mr Mohamed, a British resident, claims he was tortured
Prosecutors are being consulted over whether a criminal investigation should be ordered into UK security agents' treatment of Binyam Mohamed.
The last British resident detained at Guantanamo Bay has claimed MI5 agents were complicit in his alleged torture.
The Home Secretary referred the case to the Attorney General who is consulting the Director of Public Prosecutions (DPP), a newly-released letter reveals.
Mr Mohamed is expected to be released and return to Britain within days.
The 30-year-old alleges he was tortured into falsely confessing to terrorist activities before he arrived at the detention facility. The US denies the claims.
The letter to Andrew Dismore MP, chairman of the joint committee on human rights, was published on the Attorney General's website.
It says Baroness Scotland is consulting the DPP, Keir Starmer, over the case files.
She wrote: "I am, with the advice of the DPP, considering the material in order to determine whether there is a basis for inviting the police to conduct a criminal investigation in relation to one or more individuals.
"Any decisions on prosecutions would be reached only after such an investigation.
"At this stage no decision has been reached, and it would be premature to speculate as to the outcome of this consideration."
Baroness Scotland, a Labour peer, said she was acting "wholly independently of government and in the public interest".
It was not possible to give a precise timescale for when she would make her decision, she said.
Mr Mohamed has been held since 2002, but US charges were dropped last year.
Lawyers acting for Mr Mohamed have campaigned for alleged evidence of his torture to be made public.
Earlier this month, judges refused to order the disclosure of a summary of US reports on his detention, citing a threat to US intelligence-sharing with Britain.