Autopsies and toxicological reports released this week reveal more details about the deaths of six dairy workers — five men and one teenage boy — who died in a tragic, shocking accident at Prospect Valley Dairy outside Keenesburg on August 20.

But the information in the autopsy does not reveal what occurred that could have led to the exposure to hydrogen sulfide, which was identified as the cause of death for each of the Keenesburg Six.

The Weld County Coroner’s Office identified the victims as:

• Oscar Espinoza Leos, 17 of Nunn
• Carlos Espinoza Prado, 29, of Evans
• Noe Montañez Casañas, 32 of Keenesburg
• Jorge Sanchez Pena, 36, of Greeley
• Ricardo Gomez Galvan, 40 of Keenesburg
• Alejandro Espinoza Cruz, 50 of Nunn

Each of the victims’ autopsy reports notes that they died of “sudden death due to acute hydrogen sulfide exposure” and “history of being found unresponsive in a confined space following an industrial accident at a dairy farm.”

The accident happened on Aug. 20 at about 6 p.m., when a 45-minute call was made to 911. They were all then pronounced dead a day later, on Aug. 21, at 8 p.m. The autopsies began that day and were completed on Aug. 22, at 2:30 p.m.

The reports give scant clues about what happened to each person before he died. It does point out that most of the victims also had abrasions to their faces, hands and/or other parts of their bodies when they were brought to the coroner’s office in unsealed body bags. 

Their bodies arrived clad in jeans or dark pants, a t-shirt and boots, some wearing jewelry or a watch, the report said, adding that some also had piercings or tattoos.

The autopsy reports were completed by forensic pathology consultant Micahel A. Burson on October 8, except for the autopsy of the teenager, Oscar Espinoza Leos, whose autopsy report was signed on Tuesday, and Jorge Pena, whose autopsy was signed with two dates: Tuesday and October 8. 

Each autopsy was seven pages in length, all with the same opinion from Burton: “Based on the history provided and the autopsy findings, the cause of death is complications of acute hydrogen sulfide exposure due to an industrial accident at a dairy farm. The manner of death is accident.”

The toxicological reports indicate positive findings of thiosulfate in the amount of between 4.0 and 7.3 mcg/mL in the victims’ blood, which several online sources describe as highly and potentially lethally elevated, and likely the byproduct of the hydrogen sulfide gas.

What remains unclear is what the workers may have been doing that would expose them to not only hydrogen sulfide, but a number of other substances found in their blood, including lead, bismuth, selenium, mercury, arsenic and bromine, according to the toxicology report. 

Regarding hydrogen sulfide gas, “One of the side effects is loss of consciousness and coma,” said Dr. James Sonner, an independent consultant who gives expert testimony on toxicology and pharmacology, who was interviewed by phone from Orange County, Calif., Friday afternoon by CPR News.

The range of substances found in the blood of the victims left Sonner unsure of what could have occurred right before they died.

“They may have been working in this environment for some time, and I can’t really give you some definite reason as to why they were present,” he said of the compounds found in their blood.

He added, “They could be byproducts of manure, or fertilizers. I’d be looking into what bags of what are being brought onto the farms,” he said. He noticed that the saturation levels of methemoglobin in the workers’ blood, noted in the toxicology report, would also make it hard for their blood to carry oxygen. 

The accident was described as a “containment” accident by county coroners, and described as follows in each separate autopsy: “Reportedly, the decedent was involved in an industrial accident in a confined space at a dairy farm.” 

For Sonner, that raises the question of what space the workers were contained in, and why they were there. Previous media reports have speculated they were working in a manure pit at the time of their death; other reports have stated that one person was trapped in the pit and the other five rushed to save him against the instructions of a supervisor.

“I would wonder what that oxygen concentration in that closed environment was,” Sonner said. “If it’s an enclosed space, what could happen [is], if there’s no ventilation, they could have passed out for lack of oxygen and been unable to exit the area, and while they’re unconscious, they’re inhaling things, but it’s hard to know the primary cause of the problems they had.”

He is not the only one who remains confused by the accident and its origins. In the “History” section of the autopsy, it states, “Circumstances surrounding the accident are unclear currently.” 

The entity that could provide answers is OSHA, which is investigating the accident and has six months from the incident to give a report. 

The timeline could be impacted by the government shutdown. OSHA’s website states: “This website is currently not being updated due to the suspension of Federal government services. The last update to the site was 10/1/2025. Updates to the site will start again when the Federal government resumes operations.”