They are refusing to call it terrorism, even though the suspect is Afghan and apparently was stabbing people randomly on the street. Armed with a knife and an iron bar, he wounded seven people, and four of them are in critical condition.
This is proof that you'll still have mass murders even if you manage to wave a magic wand and take away guns. There will always be murderous people. They will commit murder even if it's just Cain, Able, and a handy rock.
I think the suit against the guard is probably BS. Even if he screwed up in some fashion, he's not responsible for the attack. The civil rights claims against the responding police officers are more interesting.
Police have no legal duty to protect people. That's well established law. Do they have the legal authority to detain people in a situation like that? Maybe temporarily, but the suit claims 10 to 12 hours. That's stretching it a lot. So is confiscating cell phones (and presumably searching them) absent probable cause.
What seems to happen in these cases is that police completely lose their shit and panic while holding everyone in the area captive until the panic fades.