Dramatic footage filmed by protesters in Sudan shows masked security agents chasing down protesters, beating them and dragging them away to secret detention centres.

Who are these hit squads? Where are these detention centres? And what happens inside their walls?

BBC Africa Eye has analysed dozens of dramatic videos filmed during the recent uprising, and spoken with witnesses who have survived torture. Some of these protesters tell us about a secret and widely feared holding facility – The Fridge – where the cold is used as an instrument of torture.

Investigation led by: Benjamin Strick, Abdulmoniem Suleiman, Klaas Van Dijken, Aliaume Leroy

Produced and edited by: Suzanne Vanhooymissen, Tom Flannery, Daniel Adamson