Just before Christmas, detectives from the Los Angeles County Sheriff's Department pried open a crate outside a warehouse to find something they had been chasing for months: an 840-pound Brazilian emerald that had been reported stolen.

Now, if they could just figure out who owns it. So far, at least five people have come forward to say it's theirs.

"It seems like the more we talk to people, the more people claim to have ownership over this thing," said Lt. Thomas Grubb, who heads the sheriff's investigative team on the case. "We haven't determined who's not a suspect, really."

Unable to determine who the real owner is, Lt. Grubb decided to keep the emerald locked up while the investigation proceeds. Meanwhile, a Los Angeles civil court is scheduled to hear from different claimants in the case on Tuesday.

Lt. Grubb, who had spent the bulk of his 26-year career conducting narcotics investigations, first got onto the case last September. A distraught man named Larry Biegler had called the sheriff's office to say that his giant emerald had been stolen from a Los Angeles-area warehouse where he had been keeping it. It was worth nearly $400 million, he said.

Lt. Grubb's detectives began investigating.

The emerald, they determined, was in the possession of two businessmen named Todd Armstrong and Kit Morrison, whom detectives tracked to a small town called Eagle, in western Idaho. When the detectives arrived in Eagle, Mr. Armstrong was in the process of trying to sell the emerald to a buyer. "We've run into a small snag," Mr. Armstrong says he told his buyer.

The Idaho men said the emerald belonged to them. They said in an interview they paid Mr. Biegler $1 million for diamonds he never delivered. Mr. Biegler had put the emerald up as collateral, they say, for the stones. When the diamonds didn't materialize, they picked up the emerald from the warehouse in Los Angeles. They showed investigators a stack of documents they said prove their claim.

Mr. Biegler — a gem broker and real-estate investor — disputes that account. He says he kept up his end of the diamond deal, and claims the Idaho men agreed to pay $80 million for the emerald, which he was willing to sell at that price.

The Idaho men agreed to turn over the emerald to the sheriff's deputies until the matter could be resolved. But the emerald wasn't even in Idaho. Mr. Armstrong and Mr. Morrison had placed it in a secured warehouse in Las Vegas for safekeeping.

Lt. Grubb began to organize an excursion to Las Vegas. On the morning detectives drove to get the emerald, he told his deputies: "We're going to stop on the way and get breakfast. We're going to pick up a $400 million piece of evidence. On the way back, we're not stopping."

When Lt. Grubb finally laid eyes on the emerald, he said, "It almost didn't look real."

Those who have seen the emerald describe it as a black boulder with protruding arm-sized green crystal cylinders. Gem experts say unbroken crystals of that size are rare. Such a large specimen usually would not be broken down into smaller pieces for jewelry. It would more likely be sold intact to a private collector or a museum. An appraisal done in Brazil valued it at $372 million, according to documents filed with the Los Angeles court.

Click over to read the full report from the Wall Street Journal.