I was going to say: he started the fire before going to work

\o

I was thinking only one who understood the smoke detector

That's totally implausible, but funny, nonetheless.

He and his wife were at work, and the kids were in school. Old one.

Sometimes when the house is too infested it needs to be burned down. Being at work is a good alibi.

I'm almost certain I saw a news story years ago for a multi family home/rental unit burned down and it was all niggers that died, but the one white family in one of the units didn't die because they were at work.