Clark is a third-generation firefighter. He's been with the Forsyth County Fire Department for 18 years.
His wife, Kari Clark, was diagnosed with cancer in 2013.
"She's the sweetest, toughest woman I know," said Matt Clark.
After finishing a 24-hour shift Tuesday, Clark picked up his wife, and they headed to the Cancer Treatment Centers of America in Newnan. They went inside at 10 a.m. By noon, his truck was gone, he said.
"So I went downstairs to get her a pillow, lunch and a blanket for infusion and my truck wasn't where I left it," said Clark.
Newnan police say they looked at surveillance footage and saw a newer model white Chevy Impala with tinted windows and a tinted tag cover pull into the parking lot around 11:50 a.m. A man got out by the Clarks' truck, police said. Two minutes later, the Impala and the Clarks' truck left the parking lot.
Clark said there were some sentimental items in the truck. His dad, who was also a firefighter, died three years ago. He also had cancer. Clark's dad's rescue knife was in that truck, along with other items that meant a lot to him. There were also medications inside that belonged to his wife.
If you have any information that can help investigators, call Newnan police. WSB-TV requested the surveillance video from Newnan police, but the station hasn't received it yet.
Clark said his truck is a 2002 white, four-door, short-bed Ford pickup truck. It has a Georgia firefighter tag No. CF615B.