An investigation into the 2011 death of two dolphins at the Connyland amusement park in Switzerland has revealed that loud music from a techno party was not to blame for Shadow and Chelmers' untimely demise, but rather a heroin subsistute, which was discovered in their urine.

A toxicology report ordered after the dolphins turned up dead following a weekend rave hosted near the park's lagoon showed traces of the semi-synthetic opioid buprenorphine — commonly used in the management of heroin dependence — were present in their system, suggesting they may have been fed drugs by partygoers.

According to Dutch marine biologist Cornelis van Elk, opiates pose a particular risk to underwater mammals as they could cause the part of the brain that regulates their breathing instinct to turn off.

Connyland keeper Nadja Gasser noted that the dolphins died a "horrendous" death that was "drawn out" for over an hour. "I have not been able to sleep since," she said.

A spokesman for the park, which has all along denied culpability for the tragic incident, says Connyland "would be asking questions" concerning prosecutors' rejection of the keepers' claim that ravers poisoned the animals.

[photo via Connyland]