Family searching for answers after daughter dies at resort during vacation in Mexico

PLAYA DEL CARMEN, Mexico -- A Wisconsin family is desperately searching for answers after their 20-year-old daughter died under mysterious circumstances at a five-star resort during a family vacation earlier this year in Playa del Carmen, Mexico.

Abbey Conner, 20, drowned in January while swimming with her brother, Austin Conner, 23, in chest-deep water at the pool in the Iberostar Paraiso Resort.

When Abbey and Austin Conner did not show up for dinner, their mother and stepfather became concerned, and they eventually learned that the siblings had been taken to an emergency room 14 miles away, Bill Conner, their biological father, who was not in Mexico at the time, told ABC News.

Austin had a concussion and a golf ball-sized lump on his head, while Abbey suffered a broken collar bone and was brain dead. Officials said they each had a blood alcohol content 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.

Mexican officials ruled Abbey Conner's death an accidental drowning, but her family members say local police refuse to investigate further into what caused her death.

"Someone needs to be held responsible for this," Bill Conner said. "It doesn't make any sense. We're lucky we didn't lose both of our kids."

The U.S. Department of State told ABC News it was "aware of the case" and extended "sincere condolences to family and friends." It said is is working to provide consular assistance but had no further comment, out of respect for the family.

"She was healthy, but for some reason she drowns in a pool," Bill Conner said. "Waist deep...it's unbelievable."

Iberostar Paraiso Resort did not immediately respond to ABC News' request for comment.