MADISON, Wis. -- A 20-year-old Minnesota man was formally charged on Friday with first-degree intentional homicide in connection with the fatal stabbing of Madison resident Joel Marino last January.

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Adam Charles Peterson was arrested at his mother's home in Grant, Minn., on Thursday. He is not fighting extradition to Wisconsin.

Madison police are calling it a "stranger killing," saying they have found no sign of any relationship between the 31-year-old Marino and the college dropout now accused of stabbing him to death at his home last January.

Peterson lived in Madison less than a year and lived on West Main Street at the time of the murder, not far from Marino's home.

Peterson also lived in other Madison neighborhoods, where residents who knew him said they're shocked to hear the news, WISC-TV reported.

Downtown residents said Peterson also lived in a neighborhood on Bassett Street.

UW students Brittany Kauffman and Alison Lancashire said news of Peterson's arrest is changing the mood of the neighborhood, WISC-TV reported.

"Just kind of scary and fearful with everything that has gone on throughout the year and knowing that someone living right next door to me could commit a crime like that, if he indeed do it. It's kind of scary," said Kauffman.

Lancashire shared similar thoughts on living next to Peterson.

"He lived next door for a while and I think his twin brother still lives next door, and we just knew those boys from around, socially. They would be here when we had parties," said Lancashire.

At those parties, neighbors remember Peterson as quieter than twin brother Eric, WISC-TV reported.

While the arrest brings some relief to the issue of safety in downtown Madison questions remain for residents who thought they knew Peterson.

"I mean, at this point it's kind of a increased suspicion I guess, of people, since this happened so close and it was somebody that we were familiar with," said Lancashire.

According to Peterson's profile on social networking site Facebook, Peterson had interests in psychology and music and lists his favorite quote as "My hope is in God."

Madeline Saxler, a friend of Peterson's from Stillwater High School in Minnesota, spoke with WISC-TV over the phone on Friday.

She described Peterson as a "quiet, but regular, person" and said everyone who knows him is very confused right now.

Saxler said that the Peterson twins were very close and that the brothers had a tough time dealing with being away from one another when Adam was in Lacrosse and his brother Eric was at UW-Madison.

Stay tuned to WISC-TV and Channel 3000 for continuing coverage.