It has been 25 years since the suspected murder of Rosemary Brown, 33 and her daughter Melissa, 15, in Adelaide.

A new reward has now been issued for anyone who has information that could lead police to solving the cold case.

The mother and daughter were last seen in Blair Athol at about 2.30am on Saturday, May 13, 2000.

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They had been living at the Windsor Gardens Caravan Park with Brown’s young son.

After the family was evicted on May 3, 2000, they moved into the caravan of another park resident at his invitation.

Three days later, all four residents were evicted from the caravan park and were forced to sleep at the Garden Island boat ramp.

The caravan owner was the last person to see Brown and Melissa.

$1 million is being offered as a reward for any information that leads police to finding the missing body of murdered teenager Melissa Brown. Credit: SAPOL

Police suspect that Melissa has been murdered with her body never found. Credit: 7NEWS

Numerous people have been questioned at length over the suspected murders — including the owner of the caravan — but there is no firm suspect.

On the day she was last seen, Brown’s handbag was discovered on Stirling St in Northfield about 14km away, but it was not handed to police until ten days later when there was a public appeal

Two months later, Brown’s body was discovered in mangroves at Garden Island, in Adelaide’s north, less than a kilometre from where she was last seen.

No details have been released to how she died.

Melissa’s has never been found, but police believe she was murdered.

“Despite the passage of time, we remain dedicated to uncovering the truth and holding those responsible accountable,” Acting Detective Superintendent Andrew Macrae said.

“We encourage anyone with information, no matter how insignificant it may seem, to come forward. Your assistance could be crucial in helping us piece together the events surrounding this tragic incident”.

There is a reward of up to $1 million for anyone who can provide information that leads to the conviction of those responsible for the pair’s murders.

Anyone with information is asked to contact police.