I'm not sure if it has been mentioned, but:
On Backup, Bob tells Thomas that the sorceres/witch didn't kill him because she wouldn't be able to hide the stench of black magic from Harry so soon after casting it. On SF, Morgan confront Harry at Sells lake house after Harry summons Toot, even grab his shoulders, and acuse Harry of killing two person (or it's people?) the night before. Had Harry really comitted such act, he would have the black magic feel on him, and Morgan should know such thing..
So there is a discrepancy, or one day is enough for the stench to go away, or Morgan dislike for Harry was so big he was disregarding evidence of Harry inocence?
I think the last option is unlike Morgan character, as shown at the end of the book. The way Harry describe Black magic foulness, I think it would last little more than a day. So I think it was something Jim hadn't decide so early in the series.