GREENWICH, Conn. (AP) – A 6-year-old boy drowned Saturday in the pool at his family’s mansion after apparently getting stuck in the drain, Greenwich police said.

The child, whose name was not released, was unconscious and unresponsive when officers arrived at 6 p.m. at the family’s home, police said. He was pronounced dead at 7:30 p.m. Saturday at Greenwich Hospital, police said.

“We’re trying to figure out what happened,” Sgt. Kraig Gray said. “For an unknown period of time, he was under the water.”

The boy, described by family members as a strong swimmer, had been playing in the family’s fenced-in outdoor pool when someone noticed he was underwater. The boy’s parents, three siblings and two family employees were home at the time, Gray said.

The death remained under investigation Sunday.