ARLINGTON — The former director of the Snohomish County Emergency Radio System ended his own life through asphyxia caused by inhaling nitrogen gas, an autopsy determined.

The county Medical Examiner’s Office on Monday confirmed the death of Mark S. McDermott, 64.

McDermott had been the focus of an expanding Lynnwood police investigation into alleged thefts of public funds. He had not been charged with a crime.

His body was found Saturday at his Arlington-area home.

McDermott was fired from the radio system in October. The public agency oversees about $25 million of public safety equipment used by first responders.

It is overseen by a board of public officials. The board president, Marysville Mayor Jon Nehring, released a statement about the death.

“The news of Mr. McDermott’s passing is extremely sad and distressing,” Nehring said. “Our hearts go out to his loved ones during this very difficult time. Because the Snohomish County Emergency Radio System (SERS) is a public agency, the investigation into the allegations will necessarily continue to its conclusion.”