4 things to know about the murder of Border Patrol agent, Air Force vet David 'Chris' Maland in Vermont

A Washington state woman charged in connection with the fatal shooting of a U.S. border patrol agent in Vermont had been in frequent contact with someone whom authorities have linked to homicides in Pennsylvania and California, according to federal prosecutors.

Teresa Youngblut, 21, faces two weapons charges in connection with the death of Border Patrol Agent David Maland, 44, who died on Jan. 20 during the shootout in Coventry, a small town about 20 miles from the Canadian border, The Associated Press reported. 

Youngblut had been traveling with Felix Bauckholt, a German citizen who also was killed, and the pair had been under surveillance for several days.

Court documents cited by The Associated Press found the gun used by Youngblut and one that Bauckholt was carrying were purchased by a third person in Vermont last February. The buyer is a person of interest in a double homicide investigation in Pennsylvania, authorities said.

Here are four new details emerging in this bizarre and tragic shooting.