TAMAP, Fla. -

Video shows Milford, Mich. native Darrin Campbell on a fireworks shopping spree just days before fireworks played a role in a massive fire at the mansion he was renting near Tampa, Fla.

On the video, Campbell is shown calmly and methodically buying many high-grade fireworks from a Tampa-area store. He bought two shopping carts full of the otherwise celebratory explosives. What didn't fit in the cart, he carried himself. He paid with cash.

Investigators say that same day -- this past Sunday -- he went to a home improvement store and bought gas cans.

On early Wednesday morning, neighbors at the exclusive community called 911 in horror. The $1.5 million home was erupting into fire. Explosions were heard, even gunshots. Four badly burned bodies were found inside.

Those bodies are Kimberly Campbell, a Dearborn Heights native, her son, Colin, 19, and her beautiful 15-year-old daughter, Megan. Darrin Campbell was found in there, too. All of them had been shot to death before burning.

Late Friday afternoon, investigators said it was Darrin -- a former Ford executive -- who shot his entire family before setting fire to the mansion and shooting himself.

"He systematically shot his son, daughter and wife in the head, placed fireworks throughout the residence, used an accelerator in lighting the fire, lit the fire and shot himself," police said during a news conference.