On 6 March 2022, ten days after Russia invaded Ukraine, huge anti-war protests took place across the country. Russia’s riot police were also out in force that day arresting over five and half thousand people, the largest number in any one day in decades.

In Moscow, one group of 29 protestors were corralled into a police van and driven to Brateyevo police station in the south-east of the city.

One by one the group were summoned into interrogation room 103 by a tall, athletic police officer dressed all in black – he refused to give his name. At least 11 of the group, all young women, were subjected to verbal and physical abuse. They were kicked, slapped, punched and choked by their abuser, the “man in black.”

Two of the women managed to secretly record audio of their ordeal on their mobile phones, and on their release shared their recordings with the media. Despite international outrage and multiple calls for an investigation, no criminal case was opened by the Russian authorities.

Feeling they had been denied justice, the women decided to take matters into their own hands and began trying to track down and identify the “man in black” themselves. They worked together, investigating a winding digital trail including leaked Yandex food-delivery orders, archived social-media accounts, and old dating profiles.

This new documentary from BBC Eye tells the story of how, after weeks of searching, the group finally found the identity of their abuser and that of his commanding officer.

The BBC put the allegations – that police officer Ivan Ryabov initiated and participated in the abuse of detainees, and that this abuse in some cases amounted to torture – to both Ryabov and Fedorinov, and to Russia’s Investigative Committee. There were no replies.

Watch the documentary: in the UK – on BBC iPlayer; internationally – on BBC World News on Saturday 10 September; and on BBC News Russian YouTube channel.

Read the story on the BBC News website - bbc.co.uk/news in the UK; bbc.com/news internationally, and in Russian on the BBC News Russian website.