PORT HURON, Mich. -

A missing 5-year-old Port Huron boy was found dead inside a car Friday afternoon not far from where he went missing.

Derrick Holmon went missing a little after 8:30 a.m. Friday.

Family members told Local 4 the boy, who had Down syndrome and a heart condition, was non-verbal but full of energy.

Holmon somehow slipped out of his home Manual Street. Police and neighbors searched the area for hours.

Holmon's grandfather, Don McCulough, told Local 4 he was becoming more frantic as the hours went on when the screams started. The little boy had climbed into a neighbor's car three houses down from his own and was dead inside.

He was inside the car more than eight hours and wasn't able to get out. McCulough told Local 4 it was impossible to see him in there because he was on the floor of the back seat. His family rushed to the car.

"One officer beat me there and he checked his wrist and I knew then. I just lost it. The officer didn't want to tell me he was dead like that but I knew," McCulough said.

Port Huron police said an official cause of death is pending but that at this point it just looks like a terrible accident.