Police in western Michigan are investigating the death of a 1-year-old boy who was found barely alive at a daycare business in Muskegon on Friday, and they suspect an 8-year-old girl may be responsible.

Muskegon police Chief Jeffrey Lewis says it was one of the worst cases he’s ever seen.

"I thought I saw everything," Lewis told MLive.com.

“This one floors me. I can hardly get a grip on it.”

The boy's mother, Bryanna Reasonover, told WXMI TV that her son, Korey Brown, was covered in bite marks and bruises, and was unresponsive when she arrived at the daycare to pick him up. He was later pronounced dead at an area hospital.

Lewis said it’s a tough case for investigators because the suspect is an 8-year-old girl and the only witness is 5.

“The 1-year-old was crying, and it appears no one was attending to the child,” Lewis said. “The 8-year-old dealt with the crying baby.”

Police said the children in the daycare had been left alone for several hours with no adults present.

The girl was taken for a mental evaluation at a hospital. The investigation into the boy’s death and how it may have happened is ongoing.