FARMINGTON — Nearly five months after 81-year-old Grace Burton was slain inside her home, police arrested a Massachusetts man they say is the killer.

Police in Waltham, Mass., Thursday night arrested Juan A. Contreras, 27, a man who advertised himself as a professional dog sitter and housekeeper while living in Farmington over the summer.

Police said DNA was a key to finding their suspect and was enough to charge Contreras with being a fugitive from justice.

Maine State Police spokesman Stephen McCausland said Contreras would be charged with murder once he is returned to Maine.

Burton was slain early in the morning June 21. Police said there is evidence she fought her attacker, possibly inflicting injuries. Burton told authorities her attacker had a thin mustache, police said.

When police arrived at her home, Burton was down on the floor of her first-floor apartment, bleeding from multiple stab wounds. Already suffering from bone cancer, Burton later died at Central Maine Medical Center in Lewiston.

The slaying rattled the community as an unknown killer roamed free. In the days following, it remained unknown whether the attack on Burton was planned or random. The attacker, police said, had cut a screen and entered through a back window.

Police had a vague description of a potential suspect, who was believed to be a small man clad in dark clothing. They interviewed more than 200 people and collected DNA from at least 70. They put up road blocks and questioned people driving through Burton’s neighborhood.

But as summer turned to fall, no arrest was made. Burton’s family raised money to offer as a reward, but still, there were no answers.

Friends and family described Burton, a mother of six, as a feisty woman who stayed up until the wee hours of morning watching television. She had lived at the apartment complex for nearly a dozen years, friends said.

Burton called 911 herself after she was attacked, police said. They believe she was able to cut her attacker, causing him to bleed — and leave crucial DNA evidence in the apartment.

Shortly after Contreras was arrested Thursday, at about 6:15 p.m., five Maine State Police detectives arrived in Waltham, preparing to bring their suspect back to face a murder charge.

Contreras was being held at the Waltham Police Department Thursday night. He was expected to make his first court appearance there on Friday.

mlaflamme@sunjournal.com