More than 10,000 prisoners held by the regime of Moamer Kadhafi have been released since the rebels captured Tripoli, but nearly 50,000 are still missing, a rebel military spokesman said Sunday.
"The number of people arrested over the past months is estimated at between 57,000 and 60,000," said Ahmed Omar Bani at a press conference in the rebel bastion of Benghazi.
"Between 10,000 and 11,000 prisoners have been freed up until now... so where are the others?"
Expressing deep concern about their fate, he said "many people in Tripoli are now discovering mass graves around former detention centres and the prison in Abu Slim."
Abu Slim, a generally pro-Gaddafi neighbourhood, has seen fierce fighting between rebels and Kadhafi loyalists.
When asked whether the missing prisoners were killed, he said "it would be catastrophic if it turns out they were killed."
"We have names of individuals who know what happened with the prisoners in Tripoli and these individuals are currently being sought by our liberation forces."
"We invite anyone who has information on prisoners to come forward, or they will be considered complicit in these crimes," Bani warned.
"It is high time those who claimed to have been too frightened to speak to come forward and testify about the crimes which were being committed."
The battle for Tripoli is almost over and the rebels are scrambling to get the capital back on its feet, but sporadic gunfire could still be heard overnight in the city.