Vargas, who has no known criminal record, set a combustible liquid on fire in his fourth-floor apartment. Building manager Italo Pisciotti, 79, and his wife, Camira Pisciotti, 69, saw smoke and ran to the unit, Zogby said. When they arrived, Vargas opened the door and fired, killing both.
Detectives were investigating whether Vargas had any ongoing disputes with the building manager, as some residents believed. His mother was not home at the time.
After gunning down the building managers, Vargas went back into his burning apartment and fired 10 to 20 shots from a 9mm pistol into the street. One of the bullets struck 33-year-old Carlos Javier Gavilanes, who was parking his car after returning home from work. Zogby said his body was found next to his vehicle.
The gunman then kicked his way into a third-floor apartment, where he shot to death Patricio Simono, 54; his wife, Merly Niebles, 51; and their 17-year-old daughter. Family members said Simono worked at a car wash and Niebles cleaned hotel rooms. Their daughter wanted to be a nurse.
All six people were killed in a short time span, Zogby said, and it is possible they were all dead by the time police arrived.
Officers and Vargas then engaged in an hours-long shootout and chase, with police following the gunman from one floor to the next.
Several hours into the ordeal, Vargas forced his way into a fifth-story unit and held two people captive. Sgt. Eddie Rodriguez said negotiators and a SWAT team tried talking with him from the other side of the door.
Miriam Valdes, 70, was in a friend's apartment two doors down. She said she heard officers trying to persuade Vargas to surrender.
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. Zogby said Vargas still had several rounds of ammunition when he was killed.
"He was ready to fight," Zogby said.
Tenants painted a mixed portrait of the gunman, some calling him a "good son" and others calling him "abusive" for how he treated his mother.
"Nobody seems to know why he acted the way he acted," Zogby said.