A leaked tooltip revealed that Captain Diomedes is now a Chaplain. While it may seem like an odd career change, it actually makes sense: In the last cinematic of Retribution's Space Marine campaign, Diomedes specifically said that he could not serve the chapter in the same manner as before. And after discovering that his lifetime of service was spent at the bidding of a traitor and a heretic, and helping to stamp out that heresy, it only makes sense for Diomedes to take on a new role as the watchman who ensures the chapter remains free of corruption.
When clicking the Servitor, one of its quotes states: "This one serves as punishment for [Redacted]". One must wonder whatever it had done to deserve its transformation into a cybernetic and nearly mindless slave.
Being caught by the Arbites stealing bread,note (Though the Arbites jurisdiction only applies if you steal bread from a kitchen tied directly to the Adaptus Terra, but they do not recognize the concept of petty crime and any action against the official governing body of the Imperium of Man is not only considered illegal but heretical) annoying the wrong member of the Inquisition, not being pious enough for the Ecclesiarchy, it could've been anything. It's a longstanding truth in 40k that just being noticed by the Imperium usually means being a servitor, being purged with promethium or being shipped out to a penal legion. At least the servitors are basically vegetables in that state.