MANASSAS, Va. (AP) — A man shot three co-workers during an altercation Wednesday at a northern Virginia business, killing two of them, before he took his own life during a police standoff along an interstate highway, police said.

Marvin Grant, 37, of Charlotte, North Carolina, opened fire at an equipment rental business in Manassas, about 30 miles (50 kilometers) southwest of Washington, D.C., Manassas Police Chief Doug Keen said at a news conference.

Keen identified the two workers who died as Richard Lamont, 48, and Christopher Serrano, 33. A third worker was in stable condition at a hospital in Fairfax, the chief said.

Grant fled in a vehicle and detectives tracked his cellphone to the Harrisonburg area, Keen said. Grant later pulled over on I-81 in Augusta County and fatally shot himself during a standoff with Virginia State Police. A state police statement said troopers did not use force.

The motive behind the shooting remains unclear, Keen said.