Police in Maine have identified a person of interest in the shooting, according to multiple law enforcement sources.
The person of interest has a history of military service and is a firearms instructor, the sources said.
The sources said he also has a mental health history, including a two-week stay this summer at a mental health facility after he allegedly made threats about carrying out a shooting at a National Guard facility.
Authorities have traced his white Subaru to a location in Lisbon, Maine, sources said.