Police are continuing to question a 49-year-old man on suspicion of murder following the disappearance of teenager Gaia Pope.
Paul Elsey, confirmed as the suspect to the BBC by his father, is from Swanage, Dorset.
Murder detectives are focussing their forensic investigations on homes, cars and an area near a coastal path where women’s clothing was found.
Mr Elsey is the third person to be held in the inquiry.
He is believed to be known to 19-year-old Miss Pope, who went missing from Swanage on 7 November.
Mr Elsey lives with his mother Rosemary Dinch, 71, who, along with her 19-year-old grandson, Nathan Elsey, was arrested on suspicion of murder on Monday.
The pair were released on Tuesday while inquiries continue.
Forensic investigations are continuing at two properties in Manor Gardens, where those arrested are believed to live. Police have also seized three vehicles.
A black jacket Miss Pope was wearing in CCTV images taken at St Michael’s Garage, Swanage, on the last day she was seen was recovered from an address in Manor Gardens.
Det Supt Paul Kessell said it was not clear who the clothes found on land near the Dorset coastal path belonged to, but they were “similar” to those Miss Pope was wearing.
Search activity involving coastguard rescue teams and Dorset and Wiltshire Fire and Rescue’s Technical Rescue Unit is focused on several fields nearby.
Miss Pope, who is from Langton Matravers, has severe epilepsy and is thought to have gone missing without her medication.
Earlier this week, her mother, Natasha Pope, urged people to look in vans, garages and houses in case she was being kept against her will.
The search for Gaia
7 November: Gaia is driven by a family member from Langton Matravers to Swanage. At 14:55, she is seen on CCTV inside St Michael’s Garage buying ice cream and at 16:00 her last confirmed sighting is at an address in Manor Gardens on Morrison Road
8 November: Gaia’s family make a personal plea through the police for her to get in contact. Ch Insp Steve White, of Dorset Police, says the force is “becoming increasingly concerned”
9 November: Dorset Police renews its appeal to find the 19-year-old. Searches have been carried out in the Swanage area, with support from the coastguard and police helicopter. Gaia’s family release a statement saying they are “frantic with worry”
10 November: CCTV footage is released of Gaia on Morrison Road at 15:39 on 7 November.
13 November: Search warrants issued at two addresses in Swanage. Rosemary Dinch and Nathan Elsey are arrested on suspicion of murder and later released under investigation
14 November: Searches continue with the coastguard and volunteers from Dorset Search and Rescue and Wessex 4×4
15 November: CCTV images of Gaia at St Michael’s Garage are released. Searches continue to concentrate inland, supported by neighbouring police forces
16 November: Paul Elsey is arrested on suspicion of murder. Women’s clothing is discovered in a field near Swanage and a police cordon is set up