A 21-year-old Washington state resident, Teresa Youngblut, was arrested for the fatal shooting of U.S. Border Patrol Agent David Maland, 44, during a traffic stop on Interstate 91 in Coventry, Vermont, near the Canadian border.

The incident occurred Monday during an immigration inspection of Youngblut’s car, which involved German national Felix Baukholt, a passenger with an expired U.S. visa.

Maland and Baukholt were killed, and Youngblut was injured.

Authorities found firearms, military-grade gear, and suspicious items, including a journal and electronics, in the vehicle, CNN has reported.

Youngblut and Baukholt had been under surveillance since mid-January for suspicious behavior.

Written by B.C. Begley