The weapon that killed Agent David Maland last week in northern Vermont was bought by a person of interest in a double murder two years ago in Delaware County, state police say.

The woman accused of shooting and killing a U.S. Border Patrol agent will remain behind bars.Teresa Youngblut allegedly shot and killed David “Chris” Maland during a traffic stop on Jan. 20 on Interstate 91 in the town of Coventry not far from the Canadian border.

As the sprawling investigation unfolds, here’s an overview of the key figures involved and their alleged connections.