Police are continuing to question two men arrested in Coventry in connection with the disappearance of a teenager in the city 21 years ago.
Detectives arrested a father and son on suspicion of conspiracy to prevent the lawful and decent burial of a body.
The pair were named locally as 74-year-old Patrick Judge and his son Keith, aged 45.
Officers from West Midlands Police searched parkland in the city for a second day after new information came to light about the disappearance of Nicola Payne, 18, who went missing in 1991.
Detectives cordoned off the patch of land behind flats on Purcell Road early on Tuesday.
A force spokesman said the initial search "uncovered areas of interest", which were investigated by 30 officers using specialist technology including metal detectors and X-ray equipment.
Specially-trained police dogs from West Midlands Police and scientists from the Home Office Centre for Applied Science and Technology (Cast) were also involved in the large-scale search.
Miss Payne went missing from the Wood End area of the city on the afternoon of December 14 1991 on her way from her home in Winston Avenue to her parents' house. Despite extensive inquiries, she has not been seen since.
In a statement released through police, Miss Payne's parents John and Marilyn said: "We hope the arrests and activity will allow anyone who may have important information to come forward and speak to the police. We can then finally find out what has happened to Nicola."
Police said officers were searching an address in Miles Meadow, Coventry, in connection with the investigation.