Insp. Reagan James says the man was arrested Wednesday for "causing a disturbance" at a medical clinic.
James says the man was cuffed and put in the back of a paddy wagon and left alone.
James says police returned 15 minutes later to find the man not breathing.
Officers did C-P-R on the man and he was taken to hospital, where he died the next morning.
James says the Alberta Serious Incident Response Team will review Edmonton police's investigation results.