Chicago officials said the treatment of a detainee in police custody is under investigation as they released video showing an officer dragging the man through a hallway.

The city late Monday released the footage showing officers' interactions with 38-year-old Philip Coleman, who was taken into custody after allegedly attacking his mother in 2012. Officials have said Coleman died later at a hospital following a reaction to an antipsychotic drug.

The video shows six officers entering Coleman's cell. One uses a stun gun. An officer then drags Coleman out by his handcuffed wrists.

A police review board previously found the officers' actions justified. But the interim police superintendent said Monday the matter is under investigation.

Mayor Rahm Emanuel said he didn't consider the case closed.

The video comes amid intense scrutiny of the department since the release of another video showing a white officer fatally shooting a black teenager.