HIALEAH, Fla. -

Pedro Vargas, 42, lived with his elderly mother on the fourth floor of the apartment complex at 1485 W. 46th Street in Hialeah, where he shot and killed six people on Friday night.

Neighbors described Vargas as a lonely man who spoke about having pent up anger. He was a gym rat and was interested in guns.

Read: Cleaners enter gunman's apartment | Memorials grow for victims

"This is the model that Vargas bought from me in 2010," said Alex Perez, who owns Florida Gun Center. "This is a Glock 17, generation 4. It's a semi-automatic pistol. The firearm that he used is a very common firearm that's used in the military and in the law enforcement."

Police said Vargas killed building manager Italo Pisciotti and his wife; Carlos Javier Gavilanes, 33; and, 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 apartment complex as terrified residents took cover in bathrooms and huddled with relatives, sometimes so close to the gunfire they could feel the shots. 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.

Vargas bought the 9-millimeter handgun in Oct. 2010. He also bought a 17-round magazine, 50 rounds of ammunition, and a Florida Dept. of Law Enforcement background check for $593.49.

Perez said Vargas took six hours of firearms training and safety courses, then received his concealed weapons permit before buying the gun.

"He was very meticulous," said Perez. "He wasn't a person that came in and just choosed a firearm and took it and said, 'I want it,' and picked it up five days from now. He read about the gun. He checked different firearms, different models."

Vargas emigrated from Cuba in 1997. He became a U.S. citizen in 2004, the same year he gradated from Miami Dade College with an associate degree in graphic design.

Employment records show Vargas freelanced at Miami Dade College, the University of Miami, and Systemax, Inc. He quit Systemax in 2009.

A spokesman for Systemax issued a statement Monday, saying: “An individual by this name briefly worked for Systemax in 2009. We express our sympathy to the victims and their loved ones."

"My gut bothers me by knowing what he did and how he did it," said Perez.