St. JOHNSBURY, Vt. (AP) -- Charges have been increased to first-degree murder against a Vermont couple charged with luring a St. Johnsbury teacher from her home and killing her in March.

Caledonia County State's Attorney Lisa Warren amended the charges against Allen and Patricia Prue on Friday saying it was a premeditated crime.

She says the Prues planned in advance to kill 33-year-old Melissa Jenkins, used the ruse of a broken down car to lure her from her home and then strangled, beat and electrocuted her with a stun gun.

Warren also says before the crime the couple bought a stun gun and a cell phone, which police say Patricia Prue used to call Jenkins.

The Caledonian Record reports prosecutors also interviewed inmates who said they have heard Patricia Prue talking about the crime.