The death of the Middlesex County deputy sheriff involved in a single-car crash in Billerica Wednesday morning has been ruled a suicide.

An autopsy revealed that the cause of death was a gunshot wound to the head, said Terrel Harris, a spokesman for the Executive Office of Public Safety.

Edward “Teddy” Dillon III, 27, of Lowell was working the midnight to 8 a.m. shift at the Middlesex House of Correction. His duties in that job included conducting routine perimeter checks of the facility and other sheriff’s department property, the sheriff’s office said in a statement Wednesday. The office would not elaborate further.

The accident occurred on Treble Cove Road at 4:10 a.m., State Police spokesman David Procopio said Wednesday.

Officials released few details after the crash, not revealing until today that Dillon had committed suicide.