UN investigators have said that accountability must be taken at the highest level after the downfall of the hardline ruler on Sunday. Here is what we know about the extent of the abuses committed:

- Caesar's photos -

In 2013 a former Syrian army photographer known by the codename "Caesar" fled the country, taking with him some 55,000 graphic images taken between 2011 and 2013.

The photos, authenticated by experts, show corpses tortured and starved to death in Syrian prisons.

Some people had their eyes gouged out. The photos showed emaciated bodies, people with wounds on the back or stomach, and also a picture of hundreds of corpses in a shed surrounded by plastic bags used for burials.

Assad's Syrian government said only that the pictures were "political".

But Caesar testified to a US Congress committee and his photographs inspired a 2020 US law which imposed economic sanctions on Syria and judicial proceedings in Europe against Assad's entourage.

In Germany and Sweden eight people suspected of crime against humanity were arrested in July in an operation codenamed "Caesar".

Germany, the Netherlands and France have since 2022 convicted several top officials from the Syrian intelligence service and militias.

UN investigators say they have lists with the names of 4,000 government officials and operatives responsible for abuses.

- 'Torture archipelago' -

Human Rights Watch (HRW) in 2012 spoke of a "torture archipelago" in which the "use of electricity, burning with car battery acid, sexual assault and humiliation, the pulling of fingernails, and mock execution" were practised in government prisons.

The Syrian Observatory for Human Rights said in 2022 more than 100,000 people had died in the prisons since 2011.

In 2023, the UN's top court, the International Court of Justice, ordered Syria to stop "inhuman or degrading treatment or punishment".

- Rapes -

In 2020, seven Syrian refugees filed a complaint in Germany saying that they had been victims of torture and sexual violence, including rape, electric shocks on the genitals, forced nudity or forced abortion between 2011 and 2013.

The UN said in 2018 there had been systmatic rape and sexual violence against civilians by soldiers or pro-Assad militias. It said an investigation had found rebels had committed similar crimes, but fewer.

On November 25, 2024, the Syrian Human Rights Network (SNHR) said there had been at least 11,553 incidents of sexual violence against women, including girls aged under 18, by the warring parties since March 2011. Some 8,024 could be blamed on the Assad government and the others mainly on the jihadist Islamic State.

- 'Extermination' -

In 2016 UN investigators said Syrian authorities were responsible for acts which came down to "extermination" and could be compared to "crimes against humanity".

It pointed to the Saydnaya prison outside Damascus, which was described in 2017 by Amnesty International as a human slaughter house carrying out a "policy of extermination".

The United States said there was a "crematorium" at the prison which was used to dispose of the bodies of thousands of inmates.

In 2022 the Syrian Observatory for Human Righs said around 30,000 people had been killed at Saydnaya, some of them after being tortured.

- Chemical weapons -

In April 2020, the chemical weapons watchdog OPCW accused the Syrian army of chemical weapons attacks in Latamne in northern Syria in 2017.

In November 2023 France issued international arrest warrants against Bashar al-Assad, his brother Maher and two generals on suspicion of complicity in the chemical attacks in August 2013 near Damascus, which according to US intelligence left 1,000 dead.

Assad's forces have also been accused of using sarin gas on the rebel town of Khan Sheikhun in April 2017, and also of chlorine gas attacks.

Assad's government denied using chemical weapons.

Israel says it has staged strikes on some chemical weapons sites this week to stop supplies falling into the hands of extremists.