The men, none of whom have been named, were questioned at police stations in Bristol and were released without charge late on Saturday night. All four were from the Bristol area. Detectives had been investigating the disappearance five years ago of Wayne
Lomas, a car dealer believed to have had connections with criminals.
The arrests followed the examination of a large concrete slab hidden under the floor of a terraced house in Southville, Bristol. The process of chipping away at the slab is expected to continue for several days before the human remains can be removed for forensic identification. It is not yet known if the remains are male or female.
The house in Greenbank Road was one of five raided by officers who had begun a re-investigation of the disappearance of Mr Lomas in 1988. It is owned by a couple, on holiday in Spain, who have been told of the discovery. Police say the couple are not connected with the inquiry.
Mr Lomas's family has also been told of the discovery. He was single and lived at Westleigh Park, Bristol. His relatives alerted the police when his home was found empty. In 1985, he was acquitted of attempted murder at Bristol Crown Court. It had been alleged he was the gunman who shot another man outside a Bristol night-club.