A Washington state woman hauling an arsenal of weapons and tactical gear was busted for fatally shooting a US Customs and Border Protection agent during a traffic stop in Vermont this week, federal authorities said Friday.

Teresa Youngblut, 21, allegedly opened fire at Border Patrol officer David Maland, 44, when he stopped her and a friend, Felix Bauckholt, Monday on Interstate 91 in Coventry, according to the FBI.

The pair was initially pulled over because Bauckholt, a German national, appeared to have an expired visa when the gunfire broke out, authorities said. 

They had been under surveillance for several days after an employee at a hotel in Lyndonville reported seeing Youngblut carrying a gun and both of them wearing all-black tactical gear.

During the shootout, Bauckholt allegedly tried to draw a gun, and one border patrol agent returned fire. Maland and Bauckholt were both shot and later succumbed to their injuries. 

The duo was allegedly hauling .380-caliber jacketed hollow point ammunition, a ballistic helmet and night vision equipment, according to court documents obtained by NBC News.

Bauckholt had been spotted by officials earlier in the day Monday wrapping objects with aluminum foil — in an apparent attempt to keep their phones from being tracked — inside a Toyota Prius in a Walmart parking lot, according to the US Department of Justice.

Maland was a US Air Force veteran from Minnesota who had reportedly been planning to propose to his girlfriend.

“Agent Maland bravely served his country as a member of the US Air Force,” FBI Special Agent Craig Tremaroli said in a press release. 

“He continued that service when he answered the call to protect and serve as a law enforcement officer, making him a shining example of service over self.”

Youngblut was charged with assault on a federal law enforcement officer.