Air accident, RAF and US investigators spent yesterday at the scene of the tragedy, which is likely to remain cordoned off until Monday.
A statement from 48th Fighter Wing said the Pave Hawk helicopter. from RAF Lakenheath in Suffolk, was performing a low-level training mission along the coast when the crash at a nature reserve happened on Tuesday night.
The investigation is being hampered because it was carrying munitions, meaning bullets are scattered around the scene, investigators said.
Norfolk Police confirmed paramedics were not needed to treat those inside the helicopter, suggesting they died on impact or soon after.
The four US crewmen who died were named by RAF Lakenheath as Captain Christopher S. Stover, Captain Sean M. Ruane, Technical Sergeant Dale E. Mathews and Staff Sergeant Afton M. Ponce.
But paying tribute to them, Colonel Kyle Robinson, 48th Fighter Wing commander, said: “The loss of our Liberty Wing brethren is felt deeply across RAF Lakenheath.
“I can only imagine the hurt and sorrow felt by the family and friends of these airmen. You are in our hearts and minds. We’re already feeling a great sense of support from across the air force and from our UK neighbours as we go through this difficult period. Thank you for keeping our airmen and their families in your thoughts and prayers.”
Tributes have been paid online to one of the four US servicemen.
Captain Sean Ruane is said to have been an experienced pilot, but it remains unclear whether he was at the controls of the Pave Hawk that came down on a marsh near Cley-next-the-Sea
Based at RAF Lakenheath with US Airforce 48th Fighter Wing, he leaves behind wife Rachel and their young son Liam. His cousin Brian Meyer tweeted: “My cousin died in a helicopter crash tonight. Pretty tore up about this. Everyone: thanks for all the kindness. I’ll pass it along to his wife and child when we see each other soon.”