UN investigators have compiled a secret list of 4 perpetrators of serious crimes in Syria and hope the fall of Bashar al-Assad will help ensure accountability at the highest level.

The coordinator of the UN Commission of Inquiry on Syria (COI) Linnea Arvidsson said that it is very important that the main perpetrators of the crimes are brought to justice, reports RFI.

"The focus must be on those who bear the main responsibility for the violations that have been committed over many years, not on the lesser perpetrators," she told French media.

The COI has collected evidence of crimes committed in Syria since the start of the civil war in 2011 and compiled a list of suspected perpetrators.

"So far we have about 4000 names on the list," Arvidsson said. The list was never made public, but investigators shared the details with prosecutors in jurisdictions investigating and prosecuting suspected war criminals from Syria.

Arvidsson said the team has "cooperated in 170 such criminal investigations", which have so far led to 50 convictions for war crimes and crimes against humanity in Syria.

"But so far they have not affected the main perpetrators. Now there is an opportunity for them to be held responsible," she added.

Damascus never gave the COI permission to enter Syria, but with Assad gone, Arvidsson said the team hopes they will now be able to gain access.

So far, the team has conducted remote investigations through thousands of interviews and studying sets of documents and other evidence.

Arvidsson said the commission has over 11 "testimonies" from victims, surviving prisoners and witnesses.

The COI hopes that steps will be taken to give the International Criminal Court jurisdiction to prosecute crimes committed in the country.

Ousted President Bashar al-Assad fled Syria for Russia on Sunday after a lightning rebel offensive, ending more than six decades of rule by the Ba'ath party.

The new government has promised justice for the victims, promising that those involved in torturing prisoners will not be pardoned, and called on countries to extradite any fugitive criminals to face justice.