After researching poisons, I decided to settle on good old cyanide. It's relatively painless if you take a lethal dose, which doesn't take much. So, basically, the dark being is going to be handing out cyanide (and water bottles?) to his victims. A painless form of suicide, which minimizes the amount of suffering that the dark being, in turn, experiences for killing cardinals. The undigested capsules will be discovered in the stomachs during autopsy, so the big question for the detectives and the Church is why cardinals are taking cyanide. I originally thought to have them wear a 666 ring and position them like an upside-down cross, but part of me wants to keep knowledge of the Antichrist's involvement completely out of the early killings and have the clues be more subtle and slow in coming out. That probably requires more deaths, which I've been trying to avoid. However, now that the deaths are all painless suicides, I may have a little freedom to kill a few more cardinals, if necessary. It would also mean losing all of scene 1.2 (Cardinal Vitale's encounter with the dark being). Regardless, the reader is ahead of the detectives since the book summary already states that the Church concludes it and Connor are being stalked by the Antichrist, so what's the point of delaying when the detectives learn the truth?
I'm going to take a crack at rewriting scenes 1.2 and 1.4 using cyanide rather than burying Vitale alive to see if I like it. Once those are written, I'll decide if I want to keep the Antichrist out of the picture completely until later.