Three American tourists found dead at their Airbnb in Mexico City last month died from carbon monoxide poisoning, officials said.

New Orleans teacher Courtez Hall, 33, and two friends — Kandace Florence and Jordan Marshall, both 28 and from Virginia Beach — were found dead in their rental unit on October 30, as CrimeOnline previously reported.

The three had gone to Mexico City for Dia de los Muertos (Day of the Dead). Neither the US Embassy nor Mexican officials have released the victims’ identities, but family members of all three have spoken out about the tragedy.

The Attorney General’s Office of Mexico City, which conducted an investigation, said that blood tests confirmed that carbon monoxide was the culprit, ABC News reported.

The office said that security guards at the residential complex in the La Rosita neighborhood noted a strong gas smell, leading investigators to initially suspect gas inhalation. The investigators found a failure in the unit’s gas boiler, which released both a gas smell and carbon monoxide, which is a colorless and odorless gas, ABC said.

A spokesperson for the attorney general’s office said that one of the victims was found dead in the bathroom and apparently had attempted to take a shower, which likely activated the boiler.

Florence’s boyfriend said he was on the phone with her on Saturday when she said she felt ill and then the call dropped. He called the Airbnb host for a welfare check, leading to the discovery of the bodies.

An Airbnb spokesperson confirmed the three friends had rented the unit through their platform.

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[Featured image: L-R, Kandace Florence/Facebook; Jordan Marshall/handout; and Courtez Hall/Facebook]