(MIRROR) — Two dolphins who died a slow and agonising death at a Swiss zoo after it hosted a weekend-long rave were probably killed by a heroin substitute according to a leaked toxicology report.
The dolphins died within five days of each other in November of last year after "Connyland" park bosses had rented land near their training pool to organisers of a weekend rave party for thousands of clubbers.
Prosecutors said at the time that they believed that antibiotics given by zoo vets were to blame for the deaths of the two dolphins at the zoo in Lipperswil, Switzerland, and they were considering negligence charges.
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But now another toxicology report has been leaked to Swiss media that was carried out at the time by the forensics institute in St Gallen - which found the heroin substitute Buprenorphin was present in the animals urine.