Abbey Conner and her brother, Austin, were found unconscious in a hotel swimming pool at the five-star all-inclusive Iberostar Paraiso Resort in Playa Del Carmen, Mexico.
Just hours into the Wisconsin family's trip Abbey and her brother were rushed to the hospital where Abbey died days later.
The family said their mom and stepdad left the two at the pool to go upstairs and get ready for dinner. When they didn't show up, they found out they had been taken to the hospital after being found face down in the pool.
Austin had a concussion and a golf ball-sized lump on his head. Abbey suffered a broken collar bone and was brain dead.
Officials said the blood alcohol level for each was around .25, three times the legal limit in their home state of Wisconsin.
Austin told investigators the last thing he remembers was taking a shot with a group by the pool.
Authorities admit there are so many unknowns and a mystery surrounding what happened that a thorough investigation is needed.
Mexican officials have ruled Abbey's death an accidental drowning but the family isn't satisfied.
The resort reportedly told the family there's no surveillance video of the incident.
The State Department told ABC News it is "aware of the case."
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