Armstrong's sister, Brigette Armstrong, said her brother called police on himself May 1.
Officers responded to a call about a possible suicide attempt about 9 p.m.
Armstrong came out of the house and said he was “seeing dragons,” according to the medical examiner's report.
He was talked into a squad car before changing his mind and going back toward the house.
When officers tried to get him back into a car, the physical confrontation ensued. At some point, he stripped off his clothes, police said.
Officers placed Armstrong in handcuffs and used belts to restrain his leg movement. The “maximum restraint hobble system” entails the use of a belt system that stops combative people from kicking, police said.
Then he became unresponsive, the autopsy report states. Tasers were not used, the report states.
Paramedics performed CPR on Armstrong. After about 40 minutes of resuscitation efforts, he was pronounced dead, according to the report.
Family members said they saw grass up his nose. They worry his oxygen supply was cut off, said his sister, Brigette Armstrong.
The medical examiner's report describes numerous abrasions on Armstrong's body, on the back of his head, his neck, his shoulders and back. It notes abrasions and marks around his wrists and ankles, where he was bound.
Some of the abrasions on his back are described as “double linear” or serrated. The Oklahoman requested but didn't receive additional information about what “double linear” abrasions look like and might cause them.
The officers involved in the arrest were Jeffery Dutton, Gregory Franklin, Mohammed Tabaia and Daniel Holtzclaw. They were placed on administrative leave after the incident, but have returned to duty, Master Sgt. Gary Knight said Thursday. Officer-involved deaths in Oklahoma City spark separate criminal and internal investigations within the police department. The criminal investigation by the department's homicide units is not yet complete, Knight said.