If I'm interpreting things right, I think they have only said that there was nothing left at the property to indicate suicide (e.g. a suicide note).Given the police have said there was nothing to indicate the sisters had wanted to disappear or harm themselves and also said it is not a criminal case, what does that leave? Some sort of accident?
We don't know all the details about what was left at the proper and why the landlady reported it so soon after. But something clearly alarmed her to alert authorities. Maybe just the circumstances of the sisters wanting to end their lease and some personal things left behind.
They've also ruled out any kind of foul play. Again, I assume that's because via CCTV they have accounted for everyone going along that path on the night.
If their aim wasn't to go into the water voluntarily, then why else would they go into that path at 2am in the morning, is the big question to find the answer to.