Darrin Campbell's odd behavior has investigators suspecting a murder-suicide

Credit: Hillsborough County Sheriff's Office/AP; Inset:PatrickMcMullan/AP

From all outside appearances, the Campbell family had it all.

Darrin Campbell had recently landed a job as the chief operating officer of a digital records maintenance company. His wife, Kim, was a former legislative aide who now focused on her family, greeting everyone at PTA meetings with a smile. Son Colin was a 19-year-old baseball standout at school, while daughter Megan, 16, was a straight-A student. They lived together in a 5-bedroom, $1.5 million mansion in Tampa, Fla., that they rented from tennis star James Blake.

“They seemed like such a normal family,” Kayla Patterson, a friend of Megan Campbell’s, tells PEOPLE. “Mr. Campbell made jokes a lot to Megan – They were sort of cheesy jokes, but he seemed to have a good relationship with her. She wasn’t scared of him or anything. He was just, you know, a dad. Mrs. Campbell was like a normal mom. Everyone in the family seemed really happy.”

But things took a tragic turn on Wednesday morning when investigators responded to a house fire and found the family of four shot to death in the burned rubble of the home. Commercial-grade fireworks were found throughout the house, and empty gas cans were recovered from an upstairs bedroom. A gun, owned by Darrin Campbell, was recovered at the scene.

Police soon began to investigate Darrin Campbell’s odd behavior in the days before the killings.

Early Sunday morning, the 49-year-old businessman drove five miles to a fireworks store, buying 12 packages of firecrackers and six packages of aerial fireworks. Wearing a dark gray T-shirt and gym shorts, he was pleasant and relaxed as he presented a 50-percent-off coupon to the clerk.

“There were no red flags,” says a store clerk. “He didn’t stand out as anyone out of the ordinary.” He paid nearly $650 in cash. Later that morning, he bought several empty gas cans from a hardware store.

In a Thursday press conference, Hillsborough County Sheriff’s office spokeswoman Debbie Carter said that autopsies were being performed. “We are not looking for any suspects,” Carter said, “not at this point in the investigation.”

Friends and family of the Campbells are trying to reconcile the seemingly happy family with such a tragic incident.

“On behalf of all in our organization we are greatly saddened to learn the news regarding our Chief Operating Officer, Darrin Campbell, and the Campbell family,” Darrin’s employer, Vastec, Inc., says in a statement. “This is a difficult time for all involved and we are trying to cope with this news.”

As the initial shock wears off, people are wondering what might have happened inside the home. “I don’t know why he would have done that,” says Kayla Patterson. “I don’t know if we’ll ever find out.”

Reporting by KEN LEE and K.C. BAKER