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.

VIDEO: Watch The Report | VIDEO: Marino's Family, Friends React To Arrest | VIDEO: Wray Outlines Info About Marino Slaying Suspect | SLIDESHOW: Joel Marino Slideshow

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.

According to University of Wisconsin officials, Peterson attended the University of Wisconsin-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.

Peterson continued to live in Madison for several months at several addresses. Peterson was in Madison less than a year, and he was living at 431 West Main St. at the time of the Marino killing, WISC-TV reported. That address is not far from Marino's home and about a block from where another unsolved slaying occurred.

UW-Madison student Brittany Zimmermann was killed at her apartment on West Doty Street in early April. Police said they haven't established any link between Peterson and the Zimmermann case.

"There is no current forensic connection between this homicide and the Brittany Zimmermann homicide," said Madison Police Chief Noble Wray.

Police said they also have no link between Peterson and the unsolved slaying last summer of Kelly Nolan, 22.

But police said there is forensic evidence linking Peterson to Marino's slaying.

Wray said that investigators submitted DNA samples from Peterson to the State Crime Lab for analysis and those samples matched those at the Marino homicide scene. Police said the DNA samples matched DNA collected from a backpack and white stocking cap found near the homicide scene in a garbage can. Wray also said that Peterson's DNA matches DNA recovered from the knife used to kill Marino.

Police said that there wasn't any one big breakthrough but rather bits of information that "snowballed" within the last week that led them to Peterson and to his arrest.

South District police Capt. Jim Wheeler was at Marino's parents' house when the call came in.

"That came in, and it was hard to describe the emotions coming though. I felt relieved. It felt good for the Marinos, that they could bring some closure to this, and it was just a good feeling," Wheeler said.

The arrest comes after an almost six-month investigation into Marino's death. The 31-year-old was apparently stabbed by an intruder in his lakeshore home on West Shore Drive on Madison's south side on Jan. 28. He was found in a nearby alley near South Park Street and rushed to a hospital but later died.

Witnesses said that a man wearing a stocking hat and Carhartt-type jacket and carrying a backpack was seen in the neighborhood at the time of the stabbing. Authorities released a sketch of the suspect in late February.

Meanwhile, friends of Peterson said they are in shock. One good friend from high school told WISC-TV that Peterson had a sort of nervous breakdown last fall when he left UW-Madison, but that he seemed perfectly normal last month.

Peterson's Father Reacts To Arrest

Peterson's father, Melvin Peterson, said he is in shock over his son's arrest in the homicide investigation.

"I'm numb; I'm in shock," Melvin Peterson told WISC-TV by phone.

He said that his son's mother is devastated about the arrest.

"Neither of us has seen this coming," said Melvin Peterson. "(This is) not the Adam Peterson we raised. (I) simply cannot believe my son committed this crime."

Melvin Peterson said Adam has a twin brother who lives in Madison and that he is also devastated by the arrest.

Melvin Peterson said that his son Adam is a "very bright, articulate, caring young man, fairly withdrawn, who I thought was nonviolent."

He said that Adam was enrolled at the UW-Madison in the fall quarter but dropped all of his classes and, after living off campus for a while, returned home.

He said that as soon as Adam returned back to Minnesota in March, he was "troubled" and "not quite the same man." He said that that Adam was seeking professional help up until his arrest and that he never mentioned anything to either him or his mother about the possible killing in Madison.

Marino's Family, Friends React To Arrest

Lou and Debbie Marino said they are emotionally exhausted but that the charging of a suspect in their son's homicide case is good news for those closest to their son.

"It's a positive thing, but it doesn't change your emotions and what your heart is going through," said Lou Marino.

Lou Marino said that even with a break in his son's killing, the pain he has felt for the past five months might never go away.

"Even though it's good news, what this does is it brings back the reality that he's gone forever, and that's the most difficult thing," he said.

In his search for answers, Lou Marino has been critical of the Madison Police Department's handling of the investigation, but on Friday he gave investigators credit.

"The police deserve the credit at this point. It took five months. Is that too long? Well, it's too long for the family but, in reality, it could've never happened, and that's what we were worried about," Marino said.

Joel's best friend, Bryan Bazan, and girlfriend of two years, Amanda Miller, said Friday that now Joel Marino's death now feels real.

"It's just nice to know someone is going to be held accountable, and that they have this person and that they don't have the opportunity to hurt anybody else," Miller said.

But Marino's friends and family said they don't feel closure. Lou Marino said it might come with time and a life sentence for his son's killer.

"We have such a hole in our heart that we'll have for the rest of our lives with our son. I can't have much compassion for this person," he said.

"I hope that he understands what he did is wrong and that he's prepared to pay for it, because it's not going to end just with going to jail. He's going to have to answer to a higher power at some point," Bazan said. "(We're faced with) the reality of everything that we'll miss about (Joel) -- grandkids, the future the family outings."

Both Lou Marino and Miller said they hope that the break in their loss will give Zimmermann's family renewed faith that her killer will also be caught.

Friends are still accepting donations for the Joel Marino Memorial Fund, which will go toward music scholarships, defibrillators and environmental conservation efforts.

They are planning a golf outing sometime in September and are looking for corporate sponsors. Those who are interested in helping can e-mail: JoelMarinoMemorialFund@gmail.com.

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