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.

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

MANCHESTER, New Hampshire ( WMUR) -- Investigators said the guns allegedly used in the killing of a Border Patrol agent in Vermont were purchased in that state. Teresa Youngblut is facing two felony charges in connection with agent David Maland's death.