Brett C. Straight, 46, was found along a bike trail on the river shoreline Monday just after 11 a.m. by someone passing the area.
The man had suffered head injuries, but an autopsy failed to determine the cause, authorities said Tuesday.
"Any time somebody dies in the public way we will consider it suspicious until we receive medical examiner reports from the coroner's office on the cause of death," Batavia police Deputy Chief Glenn Autenrieth said.
Autenrieth said they recovered a bicycle at the scene, but have not confirmed it was the man's bike.
Batavia Fire Department divers were dispatched to ensure there was "no potential evidence in the river or along the river bank," Autenrieth said.
He added that no weapon was found on the scene.
The Sun-Times Media Wire contributed to this report.