MINNEAPOLIS -- The disappearance of a ship captain as his freighter plied Lake Michigan has baffled authorities for 10 weeks, but a federal prosecutor seems confident the mystery will be solved.

Homicide, suicide and an accident remain possible explanations for Capt. Fredrich Helling's disappearance, said John Smietanka, U.S. attorney in Grand Rapids, Mich.

"We have not found his body," Smietanka said. "But we will. Someday we will."

Smietanka says he hopes an autopsy could help determine what happened to the portly, popular West German, who disappeared from the freighter Sirius in the early morning of Oct. 21. The Coast Guard searched a large area of Lake Michigan for several days, but found no sign of the 48-year-old captain.

"There is no longer an official search," Smietanka said, "but we have a constant alert out, which is customary, asking all ships . . . to be on the lookout for his body."

A property owner or beach stroller probably will find the body somewhere along the coast, Smietanka said.

Calm seas, the condition of the ship and the veteran captain's experience argue against an accident, authorities said. But investigators say they found no evidence of conflict between captain and crew and nothing that would suggest a suicide.

After FBI agents interviewed the crew, the Sirius took on grain in Duluth, Minn., and departed for Italy under the command of another West German captain flown in by the ship's agents.

Other crew members on the 579-foot freighter were British and South African.