Most of the chimpanzees that fled a preserve and mauled a group of sightseers have returned, but the leader is still on the loose "out on the hills," the sanctuary's director said Saturday.

In all, 31 chimpanzees escaped two weeks ago by using sticks to get out through a sliding metal door, said Balasingam Amarasekeran, head of the Tacugama Chimpanzee Sanctuary outside Freetown.

The chimps then attacked a taxicab of tourists, killing the driver and ripping his body apart. Another Sierra Leonean man lost his hand in the mauling on April 23. Three Americans were treated for minor injuries.

Twenty-one of the chimps have returned, but the oldest, Bruno, is "still out on the hills" with nine others, said Amarasekeran.

"We expect Bruno to be the last to return," he said.

"We never thought they could use sticks to destroy" the door, Amarasekeran said. "We are dealing with species that are very intelligent."

Chimpanzee attacks are unusual but not unprecedented.

Two chimps escaped from their cages in a California sanctuary and mauled a man in March 2005 before the man's son-in-law shot the animals to death.