A Syrian former regime official suspected of leading a notorious civilian massacre revealed by the Guardian – and who became one of the country’s most-wanted fugitives after the fall of Bashar al-Assad – has been arrested by security forces, Syria’s interior ministry announced.

Amjad Youssef was captured in the countryside about 30 miles (50km) outside the city of Hama and had “been taken into custody following a carefully executed security operation”, the interior minister, Anas Khattab, said in a social media post on Friday.

Mugshots released by the ministry showed Youssef in a striped prison uniform, while videos circulated on social media showing the former military intelligence officer in custody in a vehicle, his face bloodied, being sworn at and slapped by uniformed men.

Youssef is one of the most prominent suspects in what has become known as the Tadamon massacre, the slaughter of an estimated 288 civilians, including 12 children, in a southern Damascus neighbourhood in 2013. It was documented in a series of videos taken by the killers themselves and leaked to researchers in Europe, excerpts of which were published by the Guardian in 2022.

Warning: contains graphic images

More than two dozen videos showed uniformed Syrian army officials working with pro-government militiamen to lead groups of blindfolded civilians to the edge of a pit, forcing them inside and then shooting them dead. Their bodies were burned and buried using a bulldozer, all of it captured in detail by the perpetrators.

The footage offered an as yet unseen glimpse into the brutal treatment of civilians by Assad government forces in disputed areas across Syria, but was also extraordinary for the manner in which it emerged.

A whistleblower discovered the videos on a government laptop and secretly passed them to activists in Paris, who sent them to a pair of researchers based in the Netherlands, Annsar Shahhoud and Prof Uğur Ümit Üngör, from the University of Amsterdam and the NIOD Institute for War, Holocaust and Genocide Studies.

Over the next two years, Shahhoud and Üngör worked to identify the location of the killings, the identities of the victims as well as the perpetrators, including their alleged ringleader, a young man with a distinctive scar on his left eyebrow who they dubbed “the shadow man”.

Shahhoud eventually found a Facebook page, the profile image of which bore a resemblance to the man, which belonged to a Syrian intelligence official named Amjad Youssef. She posed as a pro-Assad researcher based in Europe and spent the next year conducting interviews with Youssef that she secretly filmed.

After the Guardian revealed the massacre in text and published excerpts of Shahhoud’s secret interviews in a two-part podcast miniseries, the US state department and the EU announced sanctions against Youssef, and France said it was commencing a war-crimes investigation.

News of Youssef’s arrest was greeted with joy in Tadamon, where mass celebrations were expected after Friday prayers.

“I don’t know what to say, I am so happy,” said Maher Rahima, a young man who lived through the era of the killings. “At the same time, I cannot forget the images of the children and women who were killed and burned. They must never be forgotten.”

Residents have said the atrocities in Tadamon continued until at least 2015, with the true death toll likely to exceed 1,000 people, many of whom were interred in mass graves around the area.

Rumours of Youssef’s whereabouts had circulated for years after Assad’s government fell in December 2024, including reports that he had fled to Lebanon or further to Europe and had undergone plastic surgery to change his appearance.

Syrian security forces finally arrested him around 125 miles from Tadamon looking much the same as he had in 2022, with the same scar on his left eyebrow, but older, frightened and bruised in the custody of a new, rebel-led government.