I don't necessarily think it's anything sinister - young healthy people die for no obvious reason all the time, so it's inevitable that eventually two young healthy people will die for not obvious reason at the same time.
It's natural to assume the worst, and it's natural to assume that because the odds are so small it's impossible for it to happen. If the odds of an apparently healthy person dying in a particular year are 1/100000, then the odds on any given day are 1/100000/365, so the likelihood of two dying together on the same day are 1/100000/365/100000/365. Small but possible.
When there is a chance of something happening, no matter how remote, then eventually it will happen. It would be stranger if it never happened.
It's obviously more likely that something untoward happened, so hopefully the police will be able to determine what happened in the future and bring whoever was responsible to justice if necessary.