HONEY, Mexico (AP) -- About 70 blue drums marked with skulls and believed to contain cyanide were found dumped in a gully in rural Mexico, ending weeks of fears that they might have been stolen by terrorists targeting the United States.

A policeman stumbled across the drums on Wednesday near Honey, Mexico, 80 miles north of Mexico City and about 420 miles south of McAllen, Texas.

Police said they now believe a hapless gang of thieves, not terrorists, were behind the May 10 hijacking of the truck carrying the sodium cyanide. Twenty other drums in the truck were recovered earlier.

"When they realized what the drums contained, they apparently dumped them off the back of a truck, because they had no use for the substance," Manuel Mendez Marin, the head of the Puebla state investigative police, told Mexican media.

"That reinforces our theory that these were people who didn't know what they were doing," Mendez said.

Sodium cyanide is used in gold and silver mining. If inhaled or ingested, it attacks the nervous system and can cause a person to suffocate within minutes.

Workers sealed off the area around the drums to begin cleaning up the poison, some of which had spilled out. Water supplies were cut off in the mountain village as a precaution against possible contamination.

"Two or three of the drums are open, and there's a kind of white substance coming out," said policeman Victor Perez Cruz, who found the drums during a morning patrol in search of a rape suspect.

Television footage showed the plastic barrels jumbled one atop another in a gully, making it hard for officials to get a clear count of them.

The initial estimate of 70 drums -- plus the 20 already recovered -- left as many as 6 unaccounted for, but at least one television network reported that Wednesday's discovery accounted for the full 76-barrel missing remnant. Altogether, the drums contained 10 tons of poison.

A heavy chemical odor hung in the air as soldiers surrounded the site. Ten people who live close to the site were evacuated, and authorities asked reporters to keep at least a half-mile away.

Health department official Rafael Martinez said the 10 people showed no symptoms of poisoning but were being kept under observation.

Experts were still testing the drums to confirm they contain cyanide, but Mexico's Defense Department said they appear to be part of the stolen shipment.

The theft had followed reports from New Zealand and Italy of cyanide threats against U.S. embassies in the wake of the Sept. 11 terror attacks.

The United States had mobilized the FBI to help in the search. On Wednesday, U.S. Commissioner of Customs Robert C. Bonner praised Mexico's nationwide effort to solve the theft.

"I am grateful to the government of Mexico for its diligent efforts to locate the drums of sodium cyanide ... and for their extraordinary assistance to help keep the U.S. Customs Service fully informed," Bonner said in a press statement.

The driver of the cyanide truck, Juan Carlos Alberto Lopez, was under house arrest in Pachuca, Mexico, after admitting to improperly leaving the main highway to take a shortcut. He also said he stopped -- also against regulations -- to help men in an apparently disabled car. He said those men pulled guns on him and stole his truck.

Police have said previously they suspect the truck hijackers were not looking for cyanide, but were common criminals who routinely hijack trucks on Mexican highways to sell their contents on the black market.

The thieves, police suggested, would have been much happier if they had found the truck full of toilet paper or detergent -- something they could sell.