Assad's infamous Syria prisons empty as rebel leader vows 'just punishment'

LONDON -- Syrian rebel leader Abu Mohammed al-Jolani said late Monday that his forces "will not hesitate to hold accountable" alleged war criminals and torturers that operated as part of President Bashar Assad's toppled regime.

Jolani -- whose real name is Ahmed al-Sharaa -- and his Hayat Tahrir al-Sham forces are the most prominent of the rebel factions that defeated Assad's government after 14 years of civil war. HTS and its ally rebel groups -- operating under the umbrella Syrian Salvation Government -- are now working to assert control of the wartorn nation.

Rebel forces offered a general amnesty for all conscripted Syrian military personnel. But Jolani said in a statement that the new authorities will seek "just punishment" for those accused of involvement in the regime's alleged human rights abuses.

"We will not hesitate to hold accountable the criminals, murderers, security and army officers involved in torturing the Syrian people," Jolani said in a statement posted to the rebels' Military Operations Command Telegram channel.

"We will pursue war criminals and demand them from the countries to which they fled so that they may receive their just punishment," he added.

Authorities will also prepare a wanted list "that includes the names of the most senior officials involved in torturing the Syrian people," Jolani said. "We will offer rewards to anyone who provides information about senior army and security officers involved in war crimes."

Crowds of rebel fighters and civilians descended on Assadist prisons as the regime collapsed during a 10-day surprise offensive. Rebel forces freed prisoners in every major city they passed through on the road to Damascus.

The most infamous facility was the Saydnaya prison in the capital, which is believed to have held thousands of people. The prison has previously been described as the "Human Slaughterhouse" by Amnesty International.

Footage from inside showed rebels and local residents surging through its corridors to free groups of men, women and children from cells.

A former prisoner at Saydnaya -- Omar Alshogre -- told ABC News that the prison "is known to have women" and that detainees there have been subjected to sexual abuse.

"Some women give birth and the children born and grew up in prison," Alshogre said. "They don't see anything but the walls of the cell. They do not know what a ball is or a bird is or a tree. This is not knew but it's always shocking to see the pictures of it."

The Syrian Civil Defence, also known as the White Helmets, appealed for information on suspected secret areas of the prison where it feared detainees were still being held. The group said it concluded its search on Monday having failed to find any "unopened or hidden areas."

"Specialized teams conducted a thorough search of all sections, facilities, basements, courtyards, and surrounding areas of the prison," the White Helmets said in a statement.

"These operations were carried out with the assistance of individuals familiar with the prison and its layout," it added. However, no evidence of undiscovered secret cells or basements was found."

The White Helmets said there are "thousands who remain missing and whose fates are unknown."

Assad fled to Russia as the rebels closed in on the capital. Kremlin spokesperson Dmitry Peskov said on Monday that President Vladimir Putin will grant his Syrian ally political asylum.

U.S. State Department spokesperson Matthew Miller told journalists on Monday that "the people of Syria are probably going to want him to return home and stand judgment for his crimes in Syria."

Asked whether Assad might stand trial at the International Criminal Court, Miller responded, "If he's not going to return home from Russia, I doubt he's going to transfer himself to The Hague, leaving Russian protection either."

ABC News' William Gretsky and Helena Skinner contributed to this report.