Short answers, pulled from the story.
The term filtration point emerged during the First Chechen War as a name for facilities illegally created to hold persons detained by federal forces. This occurred in the course of an operation to restore constitutional order in Chechnya between 1994 and 1996.
Memorial estimated that at least 200,000 people passed through established and ad hoc filtration points. This figure represents out of Chechnya's population of less than one million.
Chernokozovo detention center opened as one main facility in 1999 using a former prison building. It received significant attention in 2000 alongside European Court rulings regarding Chitayev brothers and Zura Bitiyeva cases.
Sergei Lapin was convicted in 2005 of torturing student Zelimkhan Murdalov among disappeared persons. Activists collected evidence just before demolition destroyed the building housing the cellar.
Practically all detainees faced beatings and torture according to Memorial's findings. Some individuals were summarily executed within these facilities while others served as hostages exchanged for captured Russian soldiers.