A WOMAN has been arrested in the search for the killer who opened fire on a United States Border Agent during a traffic stop.

Teresa Youngblut, 21, was charged in the killing of Agent David “Chris” Maland, 44, in northern Vermont on Monday.

She was stopped by Maland and several other agents on a highway in Coventry, which is near the US-Canada border.

Youngblut was driving a blue Toyota Prius, and she was with German national Felix Baukholt, whose visa had expired, a newly unsealed affidavit seen by NBC affiliate WPTZ states.

Agents at the scene claimed that Youngblut and Baukholt both had guns when they were stopped.

Youngblut allegedly opened fire on the agents as they approached the vehicle, and Baukholt tried to grab his gun, cops say.

Maland was struck, and agents returned fire, killing Baukholt and injuring Youngblut in their counterstrike.

Youngblut, who is believed to have fired two shots, was taken to a nearby hospital, where she remains getting treatment.

Maland was also raced to the hospital, but he was declared dead within the hour.

After clearing the scene, investigators allegedly discovered disturbing items hidden in the Prius, including a Washington ID for Youngblut.

Other than the two guns and ammunition magazines, they found cell phones wrapped in aluminum foil and several laptops.

Once the FBI arrived, they discovered tactical gear, including a ballistic helmet, a night vision monocular, a tactical belt, and hollow point ammunition.

Youngblut’s journal was found in the car alongside a package of shooting range targets and two handheld two-way radios, the affidavit states.

The duo has been under surveillance since January 14, as a hotel employee had allegedly spotted them dressed in tactical gear and carrying a gun.