On Saturday, the man and woman were both dead, along with their two young daughters, after shootings that authorities believe the man carried out. Police identified the woman as Jamie Malanowski, 28, but were withholding the names of the man, 29, and the two girls, ages 4 and 7.
The sole survivor appeared to be a 2-year-old boy, who's now recovering in a hospital.
"They were such sweet people," Montalvo said Sunday. "I've never seen an argument or a bad anything between them. They were sweet. She worked; he stayed home and took care of the kids.
If Malanowski hadn't seen her in a while, Montalvo said, she would come over and ask if she was all right.
"I'd see them sitting out back in the evenings on their little porch," she said. "The girls, I'd see them out playing in the backyard. It's so sad."
Montalvo said the couple had lived there for less than a year.
"All that's going through my head is, 'Did those kids realize what was going on?"' Montalvo said.
Erie County District Attorney Jack Daneri said the two had apparently had some kind of estrangement, and they are looking into reports that the woman might have moved out of the house.
He said the woman had left work to go to the store but also decided to check on the children, whom she was supposed to pick up that afternoon.
"She was shot when she got there; we don't know if he had already killed the two daughters and shot the son," he said.
The bodies of the two girls were found at the table, where they may have been eating breakfast, and the bodies of the man and woman were also in the kitchen, Daneri said. The boy who survived was in the living room with cartoons on but suffered only a wound to his ear, he said.
"I've been doing this for 10 years, and been to a lot of homicide scenes ... and this was just heart-wrenching. It was horrible," he said.
Courtney Jacobs, 29, said she and Malanowski had worked together since August at Crating, Handling and Transfer of Pennsylvania, a shipping company close enough to Malanowski's home for her to walk to work. Jacobs said that after Malanowski did not return from a trip to the store, she and a company supervisor became worried and went to the home.
"She was really nice. She was a sweet person; she would always help me out," Jacobs said. "She and those kids definitely didn't deserve what happened to them at all. It doesn't really need to be said, but you know."