HIALEAH, Fla. – The gunman who went on a shooting rampage at his South Florida apartment building, killing six people, was a lonely man who spoke about having pent-up anger, those who knew him said Sunday.

Pedro Vargas, 42, lived on the fourth floor of a barren, concrete apartment complex in the Miami suburb of Hialeah with his elderly mother. He rarely spoke with others there, and confided to a man who worked out at the same gym that he liked to work out his anger by lifting weights and trying to get big.

“He’d just say this was the only thing that would keep him normal, pulling out all the anger in the gym,” Jorge Bagos told The Associated Press.

Bagos said the gunman expressed frustration over bad experiences with women and losing his hair from using steroids.

On Friday night, Vargas set a combustible liquid on fire in his apartment, sending the unit into flames, police said. Building manager Italo Pisciotti and his wife went running toward the smoke. Vargas opened his door and shot and killed both of them, police Lt. Carl Zogby said.

Vargas then went back into his apartment and began firing from his balcony. One of the shots struck and killed Carlos Javier Gavilanes, 33.

Vargas then stormed into a third-story unit, where he shot and killed a family of three: Patricio Simono, 64, Merly Niebles, 51, and her 17-year-old daughter.

For eight hours, police followed and exchanged gunfire with Vargas throughout the five-story complex as terrified residents took cover. In the final hours, Vargas took two people captive in a fifth-story unit. Police attempted to negotiate with him, but the talks fell apart and a SWAT team swarmed in, killing Vargas and rescuing both hostages.

On Sunday, neighbors struggled to remember anything more than cursory exchanges with Vargas. He was often seen taking his mother, who used a walker, to run errands. Sometimes, he greeted residents and politely held open doors. Other times, he could be noticeably anti-social.

“He looked very alone,” said Isael Sarmiento, 42, who lived on the same floor as Vargas. “I saw it in his face sometimes, like he was someone who had spent many years alone.”

No one knew what he did for a living, though an email address listed for Vargas in public records suggested he had an interest in design.

On Sunday, the front door of Vargas’ apartment was half burnt and a black mix of water and ash from the blaze was scattered along the walkway.