Not sure if it fits the topic but
Warren in X of Swords. An event revolving around Apocalypse and his family and Warren, the only horseman who still carry the Apocalypse legacy, his heir and the only one addressed by Apocalypse as "son", was a glorified cameo in the first issue and then vanished.
(would've been cool to have him placed against one of the four children in the duels, possibly Death)
Not a capital crime, compared to other examples in this thread, though.