They withdrew their confessions during the trial and testified that they had been made under force, including police beatings and electric shocks.
In 2005, the nurses lodged civil suits alleging torture against 10 Libyan officers, but these were later acquitted by a Libyan court.
Bulgarian national radio aired interviews on Wednesday with two of the nurses who described how they were left to hang by their wrists for hours, were beaten naked and were given electric shocks for days on end.
Kristiana Valcheva, one of the nurses, said: "The beatings were horrendous. My body was covered with black-and-blue haematomas. Blood and lymph were flowing from my feet, but the beatings paled in comparison to the electric shocks."
Aksiniya Matosyan, the prosecutor who will oversee the case, said: "All the information contained in our preliminary investigation is hair-raising.
"The tortures applied can only be compared to those used in the Middle Ages."
If the Bulgarian prosecutors gather enough evidence against the police officers and successfully manage to convict and extradite them, the 11 Libyans could face up to six years in prison.
But a successful investigation depends heavily on co-operation on the Libyan side, which will be asked to provide materials on the case and conduct interrogations, the prosecutors said.
Rumen Georgiev of the national investigation service recently told the daily Sega: "Such a case probably seems doomed from the beginning.
"Hardly any cooperation [from Libya] is expected as their judiciary has already ruled out any guilt on the part of the officers ... The torturers have already been acquitted by a Libyan court in a similar case."
In an interview published Monday in the newspaper 24 Chassa, the son of Libyan leader Moammar Gadhafi, Seif al-Islam, said that the nurses had received unjust verdicts and that they would not be executed.