It isn't stupid at all. The strangler knows he won't be killed for it until the war is over at least.But do you think the strangler would be stupid enough to let people suspect him ? I don't think so. I'm sure he acted when he was certain they won't be able to get to him, otherwise what's the point of doing it if he's gonna get caught...
Regardless of whether the royal guards know about nen or not, it makes sense to me they'll arrest all the people in Momoze's quarters since they would be all suspects. The crime was discovered early thx to Oito, that's why evidence that it was death by asphyxiation was still fresh, however if given enough time the assassin would erase all said evidences. How? well you've said yourself, by using nen. On top of that if the royal guards are unaware of the existence of nen, then it's even better.
Everybody knows it was made almost impossible for "normal" people to attempt murder on a prince, with all the measures taken. That's why I think all the assassins chosen can come up with unorthodox methods to do task and not get caught, and what better tools than supernatural powers which the majority ignore (i.e. nen).
So my point is that if an assassin made a move, they must have acted only when they could ensure they would be out of the suspect list.
Imagine if it was Benjamin's soldier. When Benjamin gets king, he becomes free anyway,
I don't think there was a way to really do this without getting caught if it was one of the 6 guards with the way Kakin reacted.
Even if there was no evidence, what makes you think they wouldn't take all of them into custody? The 2 people sleeping at least had an alibi, it did not help them.
After all, the assassins, in their inner monologue, even wanted to make sure that they can prove to their corresponding bosses that it was them.
They WANT to leave evidence, which is probably one reason why it was so easy to conclude it must have been a clone user.
Being in custody is not a problem when there is no proof against them, because then they won't get killed off and get free when their boss wins the war.
If their boss does not win, they are probably in trouble anyway.
