SA Police have insisted members of the public are hiding information about the cold case murders of a mum and daughter after officers finished their latest search linked to the alleged killings.

Rosemary Brown, 33, and Melissa Trussell, 15, were last seen in Blair Athol in Adelaide's north at about 2.30am on Saturday, May 13, 2000.

Police say Brown was murdered and it's likely Trussell was too, but her body has never been found. 

The mother's body was discovered in mangroves at Garden Island in the city on Sunday, July 2, 2000.

Detective Superintendent Darren Fielke said this afternoon that detectives they know people are hiding something.

"Police are aware of members of the public who have information who have not come forward or have not assisted police,'' he said.

"This is the mu

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