Valdes said she heard about eight officers talking with him as she stayed holed up at the neighboring apartment. She said officers told him to "let these people out."
"We're going to help you," she said they told him.
She said the gunman first asked for his girlfriend and then his mother but refused to cooperate.
Rodriguez said the talks eventually "just fell apart." Officers stormed the building, fatally shooting the gunman in an exchange of gunfire.
"They made the decision to go in there and save and rescue the hostages," Rodriguez said. Both hostages survived.
Neighbors said the shooter lived in the building with his mother. Police don't believe she was home at the time of the shootings.
"He was a good son," Lazcano said. "He'd take her in the morning to run errands" and took her to doctor appointments.
But Valdes said he was known as a difficult person who sometimes got into fights and yelled at his mother.
"He was a very abusive person," she said. "He didn't have any friends there."
Zogby called Vargas' background "unremarkable." He said police are investigating any possible disputes between Vargas and the building manager but don't yet have any information on a possible motive. "Nobody seems to know why he acted the way he acted," Zogby said.
He said police had not responded to any prior calls at his home or found any criminal background on him.
Zulima Niebles said police told her that three of her family members were among the victims. She said her sister Merly Sophia Niebles, her sister's husband, and her sister's teen daughter Priscila Perez were all shot and killed.
Zulima Niebles' husband, Agustin Hernandez, was moving the family's things out of the apartment building and into his car Saturday. Among them were several photos, one showing the teen smiling in a red graduation gown, another of his sister-in-law in a white dress and pearls.