Orange Country District Attorney Tony Rackauckas announced Wednesday that he was charging two Fullerton, California police officers in the July 5 death of a mentally ill homeless man.

Officer Manuel Ramos faces charges of second-degree murder and involuntary manslaughter for allegedly killing Kelly Thomas. Police Cpl. Jay Cicinelli was charged with involuntary manslaughter and excessive force.

“The cause of death in this case is — it’s mechanical compression of the thorax, making it impossible for Kelly Thomas to breathe normally,” Rackauckas explained during a press conference. “In other words, the chest being compressed, Kelly Thomas was not able to inhale, and he can’t take in oxygen. Over time his brain was deprived of oxygen, and he became unconscious and went into a coma and died. That is the primary cause of death. The other injuries to the face and head contributed to the death.”

Watch this video from CNN’s Newsroom, broadcast Sept. 21, 2011.