BELFAST — Angela and Joseph Mitchell Jr. had gotten used to the parties, the noise and the arguments that came from the house next door on Waldo Avenue, about a mile from the center of town.

So when they heard two men shouting late Wednesday night, it wasn’t out of the ordinary.

But this time the shouting ended with a loud pop, followed by a woman screaming. Followed by another pop.

Joseph Mitchell called 911. Police responded within minutes, guns drawn. The couple kept their four children inside.

“I had a pretty good idea what happened,” Mitchell said.

When police arrived at 162 Waldo Ave., they found three people inside. A woman, Lynn Arsenault, 55, formerly Lynn Day, had been shot to death. Her son, Matthew Day, 22, had been shot, too, but was still alive. Another person, John Riley, was in the house but was not harmed.

The alleged shooter was nowhere to be found, but Riley and Day told police that the man they were looking for was Todd Gilday.

For several hours early Thursday morning, police searched the Belfast area looking for Gilday, 44, or his car, a silver Nissan sedan with a vanity license plate that read FOREX.

About 7 a.m., police got a tip that Gilday had checked into Penobscot Bay Medical Center in Rockport, south of Belfast. He was arrested at the hospital and taken to a local jail.

By late afternoon Thursday, Gilday made his initial appearance in Waldo County Superior Court. He was charged with one count of murder and one count of elevated aggravated assault.

Gilday spoke only briefly when asked by Judge Robert Murray if he understood the charges against him. He did not enter a plea. Gilday will be held at Two Bridges Regional Jail in Wiscasset pending a bail hearing, which will be held within the next five days unless Gilday or his counsel request more time.

Police released few details about the circumstances surrounding the shooting, but Coleman said the suspect knew at least one of the people in the home.

“This was not a random act,” he said.

An arrest warrant filed Thursday before Gilday’s court appearance shed some light on the shooting but did not address any possible motive.

According to the court document, written by Maine State Police Detective Ryan Brockway, three local police officers responded to the Waldo Avenue home shortly before 11 p.m. on Wednesday. They were met at the front of the house by Riley, who told them to hurry.

Riley told officers that he did not have a gun and that the shooter had fled.

When officers entered the home through a back deck, they saw a man lying across a woman on the floor of the kitchen. The man, identified later as Day, was bleeding from his stomach. The woman, identified as Arsenault, was “obviously deceased with what appeared to be a gunshot wound to her left shoulder and chest area,” the affidavit read.

Riley told police that a man had come to the house and was met by Day at the door. The two argued and Day tried to close the door to keep the man out of the house. Instead, the man pushed through the door, shattering the glass. He then shot Arsenault, said he was going to “kill everyone in the (expletive) house,” and then shot Day before leaving.

Both Riley and Day identified the shooter as Gilday. Neither knew why he came to the house or why he started shooting.

Gilday lived less than two miles from the scene of the shooting at Spring Brook, a large condominium complex.

Neighbors there knew little about Gilday, but he reportedly ran a financial services firm, Spinnaker Financial, out of his home, although the state Bureau of Corporations, Election and Commissions has no record of that business.

Gilday also worked briefly as a tax examiner for Maine Revenue Services, but had recently been fired from that job, according to a spokesman for the agency.

“He was in his probationary period as a new hire and he was terminated within that time,” said David Heidrich.

Gilday has an online profile on Twitter, a micro-blogging site, but he was not a regular poster. Among the businesses he followed on Twitter were weapons companies such as Barrett Rifles, Elite Ammunition, Crimson Trace and Ingalls Gunsmith.

The Mitchells said they didn’t know Todd Gilday, but they did know Arsenault. Angela Mitchell said she used to work with the woman at Bank of America, one of Belfast’s biggest employers.

Arsenault still worked at least part-time at Bank of America in Belfast and stayed with her son sometimes, according to police. The rest of the time she lived in Garland.

The Mitchells said Arsenault bought the home next to theirs several years ago. The yellow, two-story raised ranch is slightly run down. The front lawn had not been mowed recently.

“It was a party house, a drug house,” Angela Mitchell said.

The Mitchells said they called police often to report drug activity or rowdy behavior. Belfast police refused to answer questions about any past dealings with the occupants of 162 Waldo Ave. and referred all questions to Maine State Police. Spokesman Steve McCausland said he had no information about previous police activity at the house.

Gilday has no criminal history in Maine.

Mathew Day had recently been charged with aggravated assault and domestic violence assault and was supposed to make a court appearance on Thursday at Waldo County Superior Court.

His attorney, Steven Peterson of Rockport, said he didn’t find out about the shooting until Thursday morning when his client failed to show up at court. Peterson said he knew Day’s mother.

“She’s the one who retained my services for her son,” he said. “She was a real nice lady. This is a terrible tragedy.”

Arsenault had no criminal history. In 2002, she filed a protection from abuse order against her then husband, Robert Day, according to a Waldo County Superior Court clerk. The couple divorced that year.

She had remarried recently, according to Angela Mitchell.

The Mitchells, who said they didn’t sleep much Wednesday night, said they don’t know what happened inside the house other than what they have been told by police. The couple said they are devastated by Arsenault’s death but said they were not surprised by the violence.

“I’m sure this has something to do with drugs,” Angela Mitchell said.