[DaBackpack]

I'm sort of suspicious about Kanon in Episode 1. Especially the whole scene with the boiler room.

Let us say that a planned explosion is set in the boiler room. Only a few people know about it.
When Kumasawa and Kanon leave to "check the kitchen" for the source of the smell, they hear a sound from the boiler room.
While it may seem natural to assume that Kanon only wanted to prevent whoever was down there from escaping, a different idea can be presented if we assume Kanon to be a culprit (or, at least, an accomplice).

Now let us say that Kanon set up the timed explosion (he might not of; he could just be an accomplice. But the reasoning doesn't change).

He hears a sound in the boiler room and runs down there, not because he suspects that the culprit is trying to escape, but he wants to make sure that no one finds out about the trap.
After arriving, he may or may not find anyone down there. Who knows; it may have just been a delusion or a misunderstanding. The important thing is that Kanon is down there and that the others may come down there to investigate.
Kanon does not want anyone to discover the trap, so in desperation, he creates a diversion. That diversion is his own "death."
He sets up his own death (which may or may actually result in him being dead, he could have been faking it) so that the siblings do not notice anything suspicious in the room.

Another thing to bring up is Kinzo's burnt body in the basement. The perpetrator would have to know that Kinzo was dead, or they would be at least a bit startled too see the body. Thus, since Kanon is a servant and was informed by Krauss of Kinzo's death, he would not be surprised that someone tried to cover up Kinzo's corpse with the Epitaph mystery.
Either that, or it's not actually Kinzo's body. I don't know.

Edit: Random thought--- If Shannon is behind it all, then it would make sense for Kanon to avenge her. You know, since they're close.
I suspect, that since the explosion incident has been confirmed, there are two groups:
a.) Bomb squad
b.) Murder squad

While Shannon may be behind the bombings (with Kanon's help), she unfortunately gets murdered in the first twilight and can not ensure her plan's success. So Kanon takes control of the operation and makes sure that his cover isn't blown. Even if it means killing himself to do it (that's a lot of dedication for such a plan, but it could happen).

Second edit: You know, the strange smell was probably some sort of explosive fluid, like gasoline. The only reason I can back this up is because a similar thing happened in Higurashi.
When Rena went all terrorist on the school, a lot of the kids had been complaining of a smell in the school.
That sort of reminded me of this, a bit.

Perhaps Kanon remembered how the family treated Eva and Hideyoshi's deaths: they wanted to preserve the crime scene. By "killing himself," he knew that the family would not change the crime scene until the police came. So that seemed to be the best course of action for him to prevent the foiling of the trap.