LIMA, Peru -- A 29-year-old Canadian allegedly stabbed to death a British tourist after the two drank a hallucinogenic brew at a spiritual retreat in the Peruvian Amazon.

Local authorities said the incident Joshua Andrew Freeman Stevens is accused of happened Wednesday night at the Phoenix Ayahuasca spiritual retreat near the town of Iquitos.

It's not clear what led to the death of Unais Gomes, 25.

But local police chief Normando Marquez said witnesses described a fight breaking out between Gomes and Stevens during which a knife was pulled against the Canadian.

The chief said the same knife was then used by Stevens to kill Gomes.

In a video, Stevens can be seen being taken away in custody by a police truck. Martin Manrique from Iquitos' prosecutors' office says Stevens was later released but must remain in Peru while he is being investigated for homicide.

However, the Guardian reported that police concluded that all the evidence showed Stevens acted in self-defence after Gomes tried to attack him with a knife.

The British newspaper also quoted Stevens' fiancee Sarah-Anne Allen as saying all charges had been dropped and he would be returning to Canada soon.

"He is very shaken and sad, but he is coping," Allen told the Guardian in an interview posted on its website Friday.

The hallucinogenic cocktail ayahuasca, also known as yage, has been venerated for centuries by indigenous tribes in Brazil, Peru, Ecuador and Colombia as a cure for all sorts of ailments. But it's also increasingly consumed by Western tourists looking for mind-altering experiences, sometimes with deadly consequences.

The two men were guests at Phoenix Ayahuasca, a self-described "shamanic healing retreat" owned by a sister and brother team from Australia. It describes itself on its website as "a safe and supportive place to experience plant medicines and explore the true nature of the self." Phoenix didn't return emails and phone calls requesting comment.