WATERVILLE — A city man is accused of breaking into the home of a 73-year-old woman early Sunday morning and sexually assaulting her at gunpoint, police said.

Waterville detectives arrested Mark Daniel Halle, 32, at 10 p.m. Sunday night following a 20-hour investigation into the attack. Halle is charged with felony counts of gross sexual assault, burglary and aggravated assault and also assault and criminal threatening. He is being held at the Kennebec County jail in Augusta on a $225,000 cash bail.

“I’m delighted we got this monster and got him off the streets, and he won’t see the light of day again for a long time, hopefully,” Waterville Police Chief Joe Massey said Monday.

Officers were called to a home on a street off West River Road at 5 a.m. Sunday morning by a woman who said she had been attacked in her home, Massey said.

According to the woman, shortly before 5 a.m. she was woken up by a loud bang. When she went to check it out, she was confronted by a man dressed in a hooded sweatshirt and armed with a handgun. The man forced her back into the bedroom and put a pillow case over her head before sexually assaulting her, then severely beat her around the shoulders and head with the gun, Massey said. The woman suffered multiple bruises from the beating and was later hospitalized, he added.

After the attack, the man tried to clean up, demanding the woman take a shower and threatening to kill her if she called the police, Massey said. The brutality of the sudden, apparently random, attack was shocking and disturbing, Massey said.

“You think that after a lot in law enforcement nothing would shock you,” Massey said. “But this was such a vicious attack it goes to show that there are monsters living amongst us who are willing to commit such violent crimes on victims that are innocent and defenseless and then feel no remorse.”

The police who arrived at the home Sunday morning were able to identify where the attacker broke in and to discover other evidence to support the accuracy of the woman’s account, Massey said. Detectives were called in as well as the Maine State Police K-9 unit. Officers tracked footprints in the snow to a set of keys and then to a gun that they believe is the one used in the assault and which had been stashed behind a small shed at a nearby property, Massey said. The weapon believed used in the attack was a pellet gun that looked like a real firearm, he said.

“I’m sure in her mind there was no question it was a real gun.” Massey said.

Investigators eventually followed the trail to the house on Victoria Drive, where Halle was staying with his sister, Massey said. Officers interviewed Halle and “it wasn’t long in the conversation that detectives felt the guy was probably involved in the assault,” Massey said.

Halle’s sister, who was home when police interviewed him, confirmed that the set of keys were the same she had given him, Masse said. Halle was later questioned by police at the Waterville police station, where he admitted to the break-in and assault and said he had brought wire to tie the woman up, Massey said.

While Halle was being held at the station, investigators, with help from the district attorney’s office and the state police, got search warrants to cover the home where the attack took place, the house Halle was staying in and the area where the gun was found. Officers worked around the clock to gather evidence, including DNA samples and a footprint cast that “clearly linked” Halle to the assault, Massey said.

Detectives were persistent in their investigation because they did not believe there was any relationship between Halle and the woman who was attacked, and they thought he might prey on someone else, Massey said.

“We were concerned that if we did not get this guy, it could have happened again,” he said.

Investigators do not know a motive for the attack. Massey said Halle does not have a criminal history in Maine, but had only been living at the Victoria Drive address for a year and had moved around to different states a lot before that.

Despite her extensive physical injuries and trauma, the victim made a point to call police Sunday afternoon and thank them. She is being helped by family members and is getting support from sexual assault agencies, Massey said.

“It is amazing how she is holding together psychologically,” he said. “She is just going to need a lot of support in the coming days from everyone.”

Peter McGuire — 861-9239

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Twitter: @PeteL_McGuire