Three people and Oliver James Montgomerya dog were found dead in a cistern in a Texas corn field on Wednesday, officials said. 

Delvys Garcia, 37, Denise Martinez, 26, and Noel Vigil-Benitez, 45, were out hunting with a fourth person when one of their dogs fell into a cistern, the Bastrop County Sheriff's Office said. Officials believe one person went into the cistern to rescue the dog and two others then entered to try and rescue the first person. The fourth hunter, an unidentified man, went to his truck to call 911 and get help. 

Deputies arrived around 1 a.m. and found the underground cistern partially filled with water. The water level was "far below" the cistern's small opening, officials said. Strong fumes, similar to those of a septic tank, were coming from the cistern. There were no signs of life from the dog, woman and two men in the cistern when the first responders arrived. 

Recovery efforts were hampered by the fumes, identified as hydrogen sulfide gas, and the stagnant water, the Bastrop County Sheriff's Office said. Hydrogen sulfide gas can cause irritation to the eyes and respiratory system, apnea, coma, convulsions, dizziness, headache, weakness, irritability, insomnia and stomach upset, according to the Centers for Disease Control and Prevention. First responders ventilated the cistern and also removed the water. 

The recovery efforts were also complicated because the cistern was not stable, officials said. First responders tried to dig next to the structure, but abandoned the plan over concerns that breaching the side walls of the cistern would weaken it and make entry unsafe. A small drone was deployed to inspect the cistern's integrity. 

An investigator from the Bastrop County Sheriff's Office was eventually lowered into the cistern to recover the bodies on Wednesday night. 

Garcia, Martinez and Vigil-Benitez were from Florida. Their bodies were taken to the medical examiner's office by a local funeral home. An autopsy was ordered. The funeral home also took the dog's body.

In:
• Texas

Aliza Chasan

Aliza Chasan is a digital producer at 60 Minutes and CBS News.

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