District of Columbia officials are releasing police body camera footage related to the death of a special education teacher who had been taken into custody by private security guards at a Washington apartment building.

The mayor and chief of police were set to discuss the footage at a press conference Tuesday afternoon.

A spokeswoman for the city's medical examiner's office said Monday that the death of 27-year-old Alonzo Smith has been ruled a homicide, and that the cause was a heart attack complicated by "acute cocaine toxicity" and compression of his torso.

Smith died on Nov. 1.

The city said in a written statement that officers were called to an apartment building about a reported assault and arrived to find Smith handcuffed by security guards. He was unconscious and not breathing.

The video shows officers performing CPR on Smith for several minutes.

"Come on man! ... Come on buddy! ... Come on, wake up!" an officer shouts as he performs chest compressions on Smith's lifeless body.

At one point toward the end of the video, a man can be heard explaining what had happened.

"All I know is that security had to subdue him," the man says. "He was under the influence of PCP. When we found him he was already in handcuffs."