Health officials confirmed Thursday that the water at the Cecil Hotel in Los Angeles tested negative for illness-causing bacteria after the body of Elisa Lam was retrieved from a water supply tank on the building's roof.

"The findings for the tests that we did in the tank and throughout the 15 floors of the hotel all came back negative," said Angelo Bellomo, director of environmental health for the Los Angeles County health department.

Ms. Lam, a 21-year-old former University of British Columbia student, was staying at the Cecil and was last seen by staff five days after her arrival.

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She was reported missing approximately two weeks earlier.

Assistant chief Ed Winter of the Los Angeles County Department of Coroner confirmed Thursday that an autopsy had been completed, but that further testing would be required to determine whether Ms. Lam experienced organ failure or was under the influence of medications, alcohol or illegal drugs.

"The additional testing will be ongoing from this point for the next six to eight weeks," Mr. Winter said via e-mail. "Nothing will be released until we get all of the tests back."

Guest complaints about low water pressure prompted a maintenance worker to make the gruesome discovery Tuesday.

The location of the body stirred concerns over the safety of the 600-room hotel's water supply after guests bathed in and drank the water.

Health officials promptly issued a do-not-drink order that remained in place Thursday even after tests came back negative.

Mr. Bellomo explained that the health department follows the same practices regardless of whether results are positive or negative. The hotel's system will be flushed, sanitized and retested over the next several days. Until then, water is only available for flushing toilets.

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"If we get negative readings in the second round of testing, in fact, we would be ready to reopen the water service in the building," said Mr. Bellomo.

He confirmed that more than 50 guests were relocated to other hotels and around 15 refused to leave.

Officials are still trying to determine if the Vancouver woman was killed or if her death was an accident after a surveillance video that showed her pressing several elevator buttons and looking both ways out the elevator doors raised suspicions.

The Cecil Hotel is located in a rough area of Los Angeles. Efforts at gentrification often conflict with homelessness and crime. It had once been the occasional home of infamous serial killers such as Richard Ramirez, known as the Night Stalker, and Austrian prison author Jack Unterweger, who was convicted of murdering nine prostitutes in Europe and the U.S., the Los Angeles Times reported.

Alex Ristea went to high school with Ms. Lam. In an interview with CBC News, he said that Ms. Lam never drank or smoked.

"Honestly, probably one of the nicest people I knew just in terms of always caring for other people and going out there and supporting the community and volunteering for stuff," Mr. Ristea told the CBC. "Elisa would have been the last person out of all my friends I'd expected to go missing on a trip," he said.

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With a report from The Associated Press