MIAMI -- A man fatally shot four people at a birthday party early Sunday before driving home, setting his duplex on fire and killing himself, police said.

The incident happened at 2852 SW 38th Court during a party to celebrate Francisco Casas' 27th birthday.

According to police, Guillermo Lopez, 49, shot and killed his estranged wife, Lazara Mendez, his wife’s 19-year old daughter, Nayla Canfux, her daughter’s boyfriend, Casas, and the boyfriend’s grandmother, 78-year-old Maria Christ.

“Everybody started screaming, and 'Pow, pow, pow, pow, pow,' and I got up and looked and he’s coming out shooting and going back inside, shooting," said neighbor Richard Nuñez.

“It was about 20 to 22 shots in total," said neighbor Juan Sosa, who was outside walking his dog when the gunfire rang out.

The gunman was seen speeding away in a red pickup truck. Several people ran down Southwest 38th Court, screaming for help.

“He killed my mom and my sister," Andy Castillo Mendez told Local 10.

Castillo said his mother and his stepfather were getting divorced. His mother refused to reconcile and his stepfather became increasingly violent.

Several minutes after the shooting, firefighters were called to a home on Southwest 33rd Avenue that was fully engulfed in flames. A Toyota pickup truck was parked out front. Police eventually found Lopez's body inside the home, surrounded by a number of propane tanks and gas containers filled with fuel.

Police said they believe Lopez set the duplex on fire and then fatally shot himself. Investigators believe Lopez rigged the gas containers for a massive explosion.

Lazara Mendez's co-workers at the restaurant where she worked were shocked at the news of her death.

"She was a very nice woman, a good mother, a very efficient employee. We loved her. We all loved her," said Julio Varona, her boss.

Neighbors said they suspect that Lopez followed his estranged wife home from work on the night of the shootings. Varona said it was a normal night at the restaurant.

"Did she ever tell you she had a problem with her husband?" Local 10's Todd Tongen reported.

"No, because she never talked about that. It was her private life," Varona said.