(CNN) -- All four people found dead inside a burned Florida house belonging to former tennis player James Blake were shot, a local sheriff's official said Thursday.
Hillsborough County Sheriff's Col. Donna Lusczynski told reporters the medical examiner is working to determine the cause of death for two adults and two teenagers, apparently from the same family. She'd earlier said the adults were in one bedroom, while each teen was in a separate bedroom.
The father bought a large quantity of fireworks at a Phantom Fireworks location on Sunday, three days before the fire was first reported, said Lusczynski.
He bought several gas cans that same day at a home improvement store and a firearm registered to him was found in the residence, the spokeswoman added.
The fire at the Tampa home was "started intentionally by an unknown accelerant," Lusczynski said on Wednesday. Authorities found small, commercial-type fireworks inside.
Firefighters first learned of the blaze in a 911 call around 5:45 a.m. Wednesday reporting an explosion and flames.
Firefighters discovered two bodies inside the 6,000-square-foot house, authorities said. Crews later found a third body and then a fourth, the Hillsborough County sheriff's office said.
Blake, 34, was not at the home at the time of the fire and was leasing out the property, the sheriff's colonel noted.
Blake, born in Yonkers, New York, starred at Harvard before breaking into professional tennis, peaking at No. 4 in the world rankings in November 2006, according to his ATP World Tour profile.
He retired from the sport last year, and remains active with his namesake foundation and Thomas Blake Sr. Memorial Research Fund to support research at Memorial Sloan-Kettering Cancer Center.