Christopher W. Snyder, 41, shot and killed three people in his neighborhood near Brookville, Md., on May 7. (WUSA9)

Mary Ann Olson volunteered with her church, her family said. She was quick to help people on her block in the Brookeville, Md., area too, so they said it was natural for her to open her home to a neighbor fleeing her husband Monday afternoon.

Olson let the woman in, and when the husband followed with a gun, Olson tried to calm him. But in a matter of minutes, Christopher W. Snyder, 41, opened fire, killing Olson, her family friend who had just arrived from out of state for a visit and a contractor working on her deck.

Police said all three had no connection to Snyder and were simply in the wrong place at the wrong time. Afterward, Snyder retreated to his home, where police negotiators tried to coax him into surrendering for hours. At 11 p.m., officers forced their way in.

“Did they just break in the front door?” Snyder asked a negotiator over the phone, before hanging up and fatally shooting himself, police said.

Louise Tano, Olson’s sister, said Olson was artistic and loved cooking. Olson had two children and was selfless. In short, Tano said the 66-year-old died as she lived.

Christopher Wilson Snyder (Obtained by The Washington Post)

“Mary would do anything in the service of others,” Tano said. “She didn’t hesitate a second to protect this woman in need.”

Snyder’s wife told police Monday that he had held her captive in his home on a cul-de-sac on Brown Farm Way over the weekend.

Montgomery County police identified the visiting friend who was killed as Danny Lee Murphy, 70, of Brandon, S.D.; and the dead contractor as Craig Harold Shotwell, 54, of Owings Mills, Md. Snyder’s wife and two other adults managed to escape the home unharmed during the rampage.

Snyder claimed in divorce filings that he was formerly a member of the armed forces, served on classified missions and was a contractor for local law enforcement agencies, but some people who came in contact with him doubted some of those claims, and others of his assertions could not be verified. The court records showed he had a troubled relationship with the ex-wife he had divorced last year.

The Bureau of Alcohol, Tobacco, Firearms and Explosives said Snyder had a federal license to be a firearm’s dealer under the name Black Widow, and social media postings indicated he had an association with Code 3 Tactical Defense, a self-defense training gym in Columbia, Md., where one friend said he knew everyone and was frequently seen laughing and joking with clientele.

Kareem Alalfey, who said he has known Snyder for years, saw him there as recently as Thursday or Friday. He said Snyder seemed in good spirits.

“I knew he was going through some things, but he handled things well,” Alalfey said. “It’s hard for me to even wrap my head around what happened.”

Police said the violence began shortly before multiple people called 911 around 3:45 p.m. Monday to report a domestic dispute involving a gun.

Montgomery County Police Chief J. Thomas Manger said at a news conference late Monday that Snyder’s wife “took an opportunity to run out of the house and went into the neighbor’s house . . . which I think ultimately caused [Snyder] to go to that neighbor’s house.”

Tano said she doesn’t know what was said between her sister and Snyder as she tried to calm him, but the situation quickly escalated. Tano said there had never been any friction between Olson and Snyder previously.

“It’s hard to imagine this only happened in the course of minutes,” Tano said.

Todd Greenstone, a farmer who lives near Snyder’s home, said he came across Olson’s husband after the shooting as members of the local community waited at a post office for streets to reopen following the police investigation.

“My wife. I found my wife dead,” the man said, according to Greenstone.

The man explained that when he’d come home earlier, he saw Snyder walking away from Olson’s home with a long gun. Snyder turned around and looked at him. The man then went inside and saw his wife’s body, along with Murphy’s body, and saw Shotwell’s body just outside the house, Greenstone said.

Olson’s husband did not return calls for comment, and Tano said he was too distraught to talk.

Shortly after police officers arrived at the scene, they learned Snyder lived two doors down from where the bodies were found.

Heavily armed SWAT trucks arrived and negotiations wore on. At 11 p.m., “our tactical team breached the front door,” said Manger.

Officers outside Snyder’s home heard a single gunshot. He was found dead inside “from an apparent self-inflicted gunshot wound,” Manger said.

Manger said Snyder was known to police.

“We’ve had a number of contacts with this suspect in the past over a number of different issues,” Manger said, adding that his department will be releasing more details about those interactions.

Greenstone said he got to know Snyder in recent years after Snyder came to Greenstone’s farm to take part in target shooting with Greenstone’s friends. “I just didn’t care for the guy,” Greenstone said. “We do good, clean, honest shooting, some skeet shooting. He came loaded for bear.”

Greenstone said Snyder arrived once to a target shooting session with two guns holstered at his waist and another around his ankle. He also brought assault-style rifles and wanted to set up multiple targets. He spoke cryptically of working for an agency “with three letters,” which Greenstone said came across to him as nonsense.

“I asked him not to come back to the farm,” Greenstone said.

Snyder was divorced from a former wife in March 2017, according to court records. His current wife, who fled to Olson’s home, did not respond to requests for comment.

In a request to seal the 2017 divorce file, Snyder claimed that keeping the file public could put him or his family at risk because he was a veteran of the armed forces and took part in “many operations that remain classified.”

He wrote at the time he was still a government contractor and maintained a top-secret security clearance. Snyder attached letters that purported to show he contracted for local law enforcement agencies and trained deputies with the Howard County Sheriff’s Office.

A spokesman for the sheriff’s office said Tuesday the office had no record of Snyder contracting with them directly but said it was possible individual deputies used Snyder for training in a personal capacity.

Diane Jacobson, who lives around the corner from Snyder’s home, remembered meeting him several years ago when he moved into the neighborhood. He struck her as arrogant, using an insincere form of sarcasm to draw attention to his size and strength. “My name is Chris,” he said. “My friends call me ‘Little Chris.’ ”

He also alluded to his secretive career in law enforcement and offered to give Jacobson his phone number, explaining that women in his previous neighborhood had his number because he would know about trouble before the local police. Yet Snyder was always short on specifics and never directly said what he did or where he worked.

“Whenever I spoke with him, after he was done, I never really knew what he was talking about,” she said.

Friends of the victims said the randomness of the violence stung.

Matthew Thomas, 55, of Manassas, Va., said he got a call from Shotwell’s oldest brother telling him he had “bad news.” Thomas said he and Shotwell were best friends in middle and high school, growing up in Springfield, Va. The two had been friends since they were 10 years old. Thomas said he last talked to Shotwell a few days ago, when Shotwell mentioned to him that he was about to start on a big contracting job.

Thomas described Shotwell as being skilled in doing remodeling and construction work and said he’d had his own home-improvement business for at least a decade. He said Shotwell had a loving and caring personality. Shotwell would also put up videos on Facebook to give homeowners improvement tips, Thomas said.

“He’d give you the shirt off his back,” Thomas said.

Chris Justice, 47, a professor who teaches writing at the University of Baltimore, had know Shotwell for about two years after meeting him as Justice mowed his lawn in the neighborhood where both lived.

Justice, who had not heard who the shooting victims were, texted Shotwell on Tuesday at 2:16 p.m., asking “Hey, know any inexpensive plumbers looking for work?”

He had expected to get the reply he usually did: Shotwell texting back to volunteer to help.

Jennifer Jenkins and Dana Hedgpeth contributed to this report.