COLUMBIA, Mo. -- Authorities have suspended the search for a helicopter that a 911 caller said went down during the weekend with six people on board, and weighed anew whether the call may have been a hoax.

The caller -- at times sounding like he was sobbing, other times sounding disoriented -- told an emergency operator Saturday night that he was a passenger and that the pilot was dead.

Searchers combed sometimes-dense terrain west of Columbia until dark on Monday, using helicopters, planes, dogs and horses.

Sixteen square miles between Columbia and the Missouri River were combed up to four times by searchers on the ground, while planes and helicopters surveyed a 100-square mile area.

"We haven't found a thing, so we are suspending the search unless something new develops," Bruce Piringer, assistant chief of the Boone County Fire Protection District, said at midday Tuesday.

Radar images recorded at area air traffic control towers were being analyzed for the hour leading up to Saturday night's call, but the images yielded no immediate leads. Piringer said authorities were aware the call might have been a hoax, but he said he was not ready to dismiss it as a prank because wreckage from air crashes has sometimes been discovered months later.

"It's a mystery still. No one saw a helicopter go down, but we had to assume the call is legitimate and respond," Piringer said.

The caller said his name was Larry Bishop and that the flight was heading from North Carolina to Kansas City.

The call, cut off after four minutes, appeared to originate in a soybean field, authorities said.

No helicopters were reported missing; nearby airports reported no emergency calls; and there were no other reports from the public to validate the 911 call.

Rob Brown, a spokesman for the fire district, said if the call was a hoax, "someone went to an awful lot of trouble to make it seem credible by originating in a field."