That article does not, but for the curious, an investigation into the deaths (involving parties from field experts to local police) has been "essentially closed" and it was determined an unknown toxin led to the death of the two belugas. How the toxin was introduced to the tank was also not determined.

http://www.cbc.ca/news/canada/british-columbia/vancouver-aqu...

[http://vancouversun.com/news/local-news/vancouver-aquarium-p... article on the Aquarium's formal report)

---

The aquarium now suspects that a toxin is responsible, although no lingering contaminants have been found in the tissues of the dead whales. While intentional poisoning hasn’t been ruled out, it’s also possible that a naturally occurring toxin is responsible.

“The epidemiology of the scenario, the chain of events, lead us to be highly suspect of a toxin that came and went — and one that we may not identify,” Haulena said.

---

Investigation continues, but it's a small town and the unproven truth is that one of the people behind this ban poisoned the two whales to 'save them'