It's whale vomit - known as ambergris, which is still sometimes used to make perfume.
McAfee's home on Ambergris Caye, an island off Belize's mainland, was raided after Faull's death.
McAfee lives in the remote northern part of Ambergris Caye, an island 36 miles from the Belize mainland.
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Charlie Naysmith found the 600g lump of ambergris in a patch of seaweed at Hengistbury Head in Bournemouth.
Ambergris is found in the innards of the sperm whale and used in perfumes after it has been vomited up.
Charlie says he has already made plans for what he will spend the money on if they can sell the ambergris.
The hard beaks of giant squid, a main source of food for sperm whales, have often been found inside lumps of ambergris.
Ken Wilman found the ambergris while walking his dog on the beach.
Mr Faull was found on Sunday with a gunshot wound to his head at his home on the tiny island of Ambergris Caye.
Several years ago, he had bought a house on Ambergris Cay in Belize that had been damaged in a hurricane, the family said.
Ambergris is a natural excrement thought to be used by the whale as a digestion aid and is expelled from its abdomen often while hundreds of miles away from land.
Belize authorities say they only want to talk to McAfee about the November 11 shooting death of American businessman Gregory Faull, who was found dead in his home near San Pedro, on the Caribbean island of Ambergris Caye.
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