The owner of a Setauket tree-trimming company died of injuries after the tree he was working on Monday cracked and split apart at a Stony Brook preserve, Suffolk police said.

Erik Halvorsen, 45, was pronounced dead at Stony Brook University Hospital, police said.

Halvorsen, the owner of Norse Tree Service, was in a harness 50 feet up a tree he was trying to cut down at about 11:15 a.m. at the Avalon Park and Preserve, police said.

Suddenly, the tree trunk splintered and trapped Halvorsen against the tree, police said. Halvorsen was wearing a safety harness and attempted to free himself but fell 20 feet. A co-worker was able to lower Halvorsen to the ground, police said.

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An ambulance transported Halvorsen to Stony Brook University Hospital where he was pronounced dead, police said.

Homicide detectives were investigating. Parks officials could not be immediately reached.