After thoroughly searching the inside of a volcanic crater, Red Cross rescuers are ending their hunt for a Chicago-area man who disappeared in a national park in Costa Rica.

Hopes had been lifted Monday when possible human remains were spotted in a crater, but officials said Thursday that what they thought was a body ended up being red foam.

Friends and family of David Gimelfarb are continuing to search for the 28-year-old doctoral student in psychology, who grew up in Highland Park, Illinois

"We sympathize with the family of David Gimelfarb," said Costa Rica Red Cross President Miguel Carmona. "We talked to them and explained the lamentable results were not positive. They understood the situation and appreciated the effort."