[fnky]

But there's no way they can prove that it was actually the owner that did this. An argument could be that someone got access to the WiFi, either maliciously or otherwise.

It's not enough to be used as evidence in court.

Most likely did the majority of the bots use proxies and VPNs, which may or may not provide additional information about their customers, but even then it has to be proven that is was the same user that did the acts which is very difficult.

[WillPostForFood]

It is enough to be used as evidence, it isn't enough, by itself, to definitively prove identity. It might be enough to get a subpoena to image the computers at the IP address. From there you might find the offending material that was broadcast, VPN accounts, chat logs talking about planning it, etc...