The Denver Office of the Medical Examiner performed an autopsy on Wednesday but said that the cause of death for 29-year-old Alonzo Ashley is still pending and needs further investigation.
Ashley is accused of threatening his girlfriend at the zoo on Monday afternoon and Denver Police was called when he allegedly attacked a zoo security guard.
When officers arrived, police say Ashley continued to resist arrest, and officers used a stun gun to help subdue him.
After he was subdued, police say Ashley started to convulse and stopped breathing. He was taken to Presbyterian/St. Luke's Hospital where he was pronounced dead.
Police say drugs and drug paraphernalia were found on Ashley.
His family disputes the claim that he was fighting against officers during the confrontation.
Police are still looking for witnesses to the incident and are asking them to call 720-913-6050.
(KUSA-TV © 2011 Multimedia Holdings Corporation)