Britain's Foreign Office said Saturday that it was aware of the death of a British national in Colombia on Wednesday.
Miller drank yage, a psychedelic brew produced from various plants native to the Amazon, during a ritual led by a local shaman, Suarez told The Associated Press. Suarez said such rituals are popular in the Putumayo and Amazon regions of Colombia "for the effects caused by the drink, especially hallucinations."
After Miller's health deteriorated, Suarez said, the shaman sent him to a hospital on a motorcycle, along with two young local men.
Miller "died on the way. Everything indicates that the two young men panicked and left him on the side of the road," Suarez told The Associated Press.
Suarez said investigators have identified and questioned the two men and the shaman, but they have not yet been arrested for any crime. He declined to reveal the names of the three.
Suarez said nationals of Italy, Germany, France and Colombia also participated in the ritual.
Fellow traveler Christopher Dearden told the Daily Mail newspaper that Miller had a bad reaction to yage.
Miller's body was at a Mocoa medical center Saturday and had not been formally claimed by his family. The director of the center, Antonio Avila, said an autopsy was performed Thursday but he was not authorized to reveal details.
Carlos Eduardo Valdez, the head of Colombia's medical forensic institute, said the autopsy showed no signs of violence against Miller. He said toxicology samples have been sent to Bogota for analysis to help determine the cause of death.
Suarez said he did not know when Miller arrived in Colombia but said he had had visited an archaeological site in southern San Agustin before traveling to Mocoa, about 475 kilometers (295 miles) southwest of Bogota.
Associated Press writer Jill Lawless in London contributed to this story.