A HH-60G Pave Hawk helicopter had taken off from the U.S. Air Force-operated Lakenheath Royal Air Force base in England for a routine training mission after dark Tuesday when in crashed in a nature reserve on the Norfolk coast, the Wall Street Journal reported.
The helicopter's four crew members, identified as Capt. Christopher Stover, Capt. Sean Ruane, Technical Sgt. Dale Mathews and Staff Sgt. Afton M. Ponce, were killed in the crash.
Police determined the case was not criminal and handed the investigation over to the U.S. Air Force and British Ministry of Defense.
U.S. Col. Kyle Robinson, 48th Fighter Wing commander, said Thursday the cause of the crash had yet to be determined.
"It is still too early to speculate as what caused the crash and make any long-term decisions based on that," he said.
A senior officer with Norfolk police said investigators are considering "different scenarios" with a bird strike one possibility, the Daily Telegraph reported Thursday.
Pink-footed geese, which breed in Iceland and Greenland, winter on the East Anglian coast with hundreds at the 800-acre sanctuary. Local residents say large flocks are often on the move in the early evening when the crash occurred, returning to their roosting areas.
"It may well have been that the crash was caused by geese," said Sue McKnespiey, owner of Cookies crab shack in nearby Salthouse. "They are always flying low overhead at this time of year and they are often in big flocks of a couple of dozen or more."