Killing someone while they're Sleeping isn't a good idea. Killing them with magic while they're Sleeping is even worse.
Thom doesn't realize that until the day of Jonathan's coronation, when the earth lurches and the roof collapses and Thom sees Roger standing right behind the king, but no one else notices and no one else does anything and all Thom can hear over the sound of the world shattering is a low, low cackle.
Everyone else just says it was an earthquake, and Thom wonders at their blindness before he realizes that the old duke doesn't say that, and the thief whose heart Alanna broke doesn't either. A few other people are silent, too, and it is then Thom realizes that no, his familial insanity really hasn't sprung up in him; only the people with magic saw Roger.
He wonders, a bit, why Alanna didn't, but he knows her powers of denial. It shouldn't surprise him that she refuses to notice.
King Jonathan dies a month after his coronation, after a month of crumbling walls and flying cutlery and sudden mid-step falls, and when Thom bursts into the dead king's room, he is unsurprised to see Roger still sitting with his hands around Jon's strangely unbruised throat.
Thom is quite surprised to see Jon, standing next to his own deathbed, smoking with a deep-rooted rage that has set the floor to trembling. Thom's stare jerks to Roger, who is watching him with mocking mirth in his eyes and wicked glee in his smile, and Thom turns on his heel and runs all the way to the catacombs.
Roger's crypt is a dark, dark void, and the place is thronged with the faces of the dead.