Flames engulf a house owned by former tennis star James Blake in Tampa, Florida. Picture: Hillsborough County Sheriff's Office, via Reuters

Tampa -

A man, his wife and their two teenage children were shot before the home they were renting from a former tennis star burned down in what investigators called arson, with fireworks and gasoline perhaps contributing to the fire, authorities said on Thursday.

Autopsies were still being completed to determine how the four died, but investigators have said they are looking into the possibility of a murder-suicide.

Authorities recovered a gun at the home registered to Darrin Campbell, and he bought an “exceedingly large amount” of fireworks and gas cans days before the fire, Hillsborough County Sheriff's Colonel Donna Lusczynski said.

Authorities still have not positively identified the bodies, but the family has not been accounted for, and a relative said they were inside the home when it burned.

As flames shot through the roof on Wednesday morning, neighbours reported explosions.

Campbell bought $650 of fireworks on Sunday, and authorities said fireworks were found throughout the home. Still, it wasn't clear what role the fireworks might have played, though Lusczynski said they could've been used to ignite the fire or keep it going.

The home is owned by former tennis professional James Blake.

William Weimer, vice-president of Phantom fireworks, described them as fireworks someone might set off on Independence Day.

Weimer said the fireworks could have started a fire, but it would have spread slowly. The amount of powder inside each one was smaller than an aspirin, he said.

A store manager, Rocky DiRoma, said there was nothing unusual about Campbell during the $650 purchase.

“He was just an average Joe,” DiRoma said.

A former neighbour, George Connley, said Kimberly Campbell was “sophisticated and classy”.

“We know nothing of any problems,” Connley said. “The kids were outstanding children. This is very difficult to put our arms around.” - Sapa-AP