Last Updated May 7, 2014 8:55 PM EDT
The victims were described as two adults and two teenagers, but they have not been positively identified, Hillsborough County Sheriff's Col. Donna Lusczynski said.
She called the fire as "unusual" and said there were "various fireworks" throughout the nearly 6,000-square-foot home in Avila, an exclusive community north of Tampa.
Two of the bodies appeared to have "upper-body trauma," Lusczynski said, but she didn't indicate which ones or give any more details.
The teens' bodies were found in their respective bedrooms and the two adults were found in one bedroom, she said.
She also said no weapons had been found and that murder-suicide was a possibility.
Former tennis star James Blake had been renting the five-bedroom, five-bathroom home, valued at more than $1 million, to a family for about the past two years, Lusczynski said. Blake was not there at the time of the fire.
The Tampa Bay Times said voter records identify the address as the home of Darrin James Campbell and his wife, Kimberly Ann Campbell. Their two teenage children, Colin and Megan, were students at the private Carrollwood Day School.
A neighbor told CBS affiliate WTSB that the Campbells had not been seen since Tuesday and called them "the nicest people you'll ever meet."
A former neighbor, George Connley, told The Associated Press that Darrin Campbell was the treasurer at the school his children attended. Word of the fire sent shock waves among students and staff.
"The tenor of the school is sadness," Ryan Kelly, head of Carrollwood Day School, told the Tampa Bay Times.
At one time, Darrin Campbell was the senior vice president at PODS, a company that provides mobile, temporary shipping and storage containers. According to his LinkedIn profile, he left PODS in 2007 and was a vice president at IVANS, an insurance company.
IVANS was purchased by another company and Campbell no longer worked there, said Matt Fogt, a spokesman for the new company, Applied Systems, who was reached by telephone.
"They were a very nice family. We know nothing of any problems," Connley said. "The kids were outstanding children. This is very difficult to put our arms around."
He said that Kimberly Campbell was "sophisticated and classy."
The fire was reported about 6 a.m. Wednesday. Video showed the house totally engulfed in flames.
Lusczynski said it took firefighters several hours to extinguish the blaze as hot spots continued to pop up and the fire kept restarting. Investigators were able to finally get inside of the mansion around 3 p.m.
Blake bought the home in the Avila subdivision in 2005 for $1.5 million, according to Hillsborough County property records.
Avila is an exclusive enclave known for its mansions and heavy security. Many well-known athletes call the community home and over the years, various football, baseball and tennis players have bought homes in the subdivision, which has a country club and golf course.
Blake, 34, was ranked fourth on the ATP world tour in 2006. He retired last year. He also has the James Blake Foundation, an organization dedicated to cancer research, in memory of his father who died of gastric cancer.