MADISON, Wis. (AP) -- Madison police are calling it a "stranger killing."

They've found no sign of any relationship between 31-year-old Joel Marino and the college dropout now accused of stabbing him to death at his home last January.

A charge of first-degree intentional homicide was filed Thursday against 20-year-old Adam Peterson, who was arrested at his mother's home in Grant, Minnesota. He is not fighting extradition.

According to University of Wisconsin officials, Peterson attended the UW-La Crosse before transferring to UW-Madison last fall as a junior, but he dropped his classes in October and officially withdrew from the university in November.

He continued to live in Madison for several months at several addresses, including one about a block from where another unsolved murder occurred. 21-year-old Brittany Zimmermann was killed at her apartment in April.

Police say they haven't established any link between Peterson and the Zimmermann case.

They also have no link between him and the unsolved murder last summer of 22-year-old Kelly Nolan.