Six of Queen Elizabeth's swans have been stabbed and beheaded.
Queen Elizabeth
The majestic birds, which are protected under the monarch's royal prerogative, were found mutilated in Birchmere Park, Thamesmead, south-east London, last month.
The RSPCA are investigating the shocking murders and have setup 24-hour patrols, with the help of the locals, around the area to help catch the catch the violent killers.
Park rangers have refused to give the dates of when the bodies of the swans - including a Canada Goose - were found, but the RSCPA was made aware of the deaths on December 6 - although they think the incident took place two weeks prior.
Nick Wheelhouse, RSPCA inspector, told the BBC: "It's really concerning because the birds seem to have been stabbed and then beheaded, with their bodies left beside the water. While it's a serious animal welfare concern it's also really upsetting for any of the park users who make the grisly find."
Paul West, who is part of the local swan protection patrols, added: "This is an act of wanton cruelty and evil. It is beyond belief.
"We keep in the shadows and use torches only when we need to. So we try to keep a low profile in the attempt that we catch them in the act."
The Metropolitan Police are helping the RSPCA with the investigation as under the Wildlife and Countryside Act 1981, anyone prosecuted for deliberately trying to injure, kill or take a wild bird can face up to six months in prison and a £5,000 fine.
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