The two suspects involved in the fatal shooting of a Border Patrol agent were armed and equipped with tactical gear, including night vision goggles, and had been under the surveillance of federal authorities for nearly a week, according to newly unsealed court records. The suspects have been identified as Teresa Youngblut, a 21-year-old from Washington, and Felix Baukholt, a German citizen who the FBI said was in the U.S. on a visa. Prosecutors allege that Youngblut pulled a handgun and fired in the direction of border patrol agents without warning, prompting a shootout that left both Baukholt and agent David “Chris” Maland dead. But authorities have not yet said who they believe fired the bullet that killed Maland. Youngblut has been charged with two federal crimes: using a deadly weapon during an assault and interfering with border patrol agents during their official duties. An FBI affidavit written in support of those charges offers the clearest account yet of the circumstances leading up to the fatal traffic stop but provides little insight into what the suspects were doing in northern Vermont. Investigators began performing periodic surveillance of Baukholt and Youngblut sometime around Tuesday, January 14, after an employee at the Lyndonville hotel where they were staying called to report concerns. The caller informed law enforcement that the two were wearing what appeared to be all-black, tactical-style clothing and that Youngblut was wearing a holstered firearm. Vermont State Police and Homeland Security investigators made contact with the two shortly after. They declined to “have an extended conversation,” claiming simply that they were in the area to look at purchasing property, the affidavit says. The pair checked out of the hotel later that day. Five days later, on January 19, investigators observed them in “similar tactical dress” walking in downtown Newport. Youngblut was still carrying a handgun at the time, the affidavit says. [content-1] On January 20, in the hours before the shooting, investigators observed Baukholt go into the Walmart in Newport and purchase two packages of aluminum foil. He returned to the blue Prius they were driving and was seen removing sheets of foil around an object; investigators would later find tin-foil-wrapped cellphones in the vehicle. Later that afternoon, the affidavit says, Border Patrol agents conducted the stop to perform an “immigration inspection” because it appeared Baukholt — the Prius’ registered owner — had an expired visa. An FBI statement issued…