This gold box by Bill Reid with a sculptured eagle on top was one of 15 art objects stolen from the UBC museum. (UBC Museum of Anthropology)

RCMP believe the 15 pieces of artwork stolen from UBC's Museum of Anthropology are still in the Lower Mainland, and hope to speak once more to a tipster who didn't leave a name.

"We want to appeal to a tipster who provided us with information in the past, as we believe this person may have more information that could further the police investigation. We're talking here about national treasures," said Const. Annie Linteau.

Twelve works of gold jewelry by Haida artist Bill Reid and three Mexican necklaces made up of gold coins were stolen from the museum overnight May 23.

Police now believe the thief or thieves may be trying to sell the artwork through a network of criminal associates in Greater Vancouver, but investigators also haven't ruled out the possibility international art thieves may be involved, said Linteau.

The investigators believe it's unlikely the pieces will be melted down, because of their value in the art world, Linteau said.

The museum's insurance company has substantially increased the $50,000 reward for information leading to the recovery of the pieces according to Linteau, but she could not say by how much.

But police hope the growing reward will result in another break in the case, she said.