obviously didn't do the murder, as his interrogation dialogue suggests (and is backed up by comments made by the person he threatens in the garden) . I've unlocked all the dialogue triggers I can find for the quest, and although
he was contracted by a third party (and Antonius knew about this, and is probably more guilty given
"Just keep Bridget a virgin" is zero help, and not even the best choice - you should unlock Heather and stick to anal, she still agrees to move to your house and Bridget's Love score cannot be raised unless you're cream pieing for ze babies. If you want to max all scores Love/Corruption, sleep with Heather (no vaginal), sleep with GILF, sleep with Bridget (vaginal only to raise Love). This solution maxes all chars and keeps the inquistion ending.
Which I already knew, but locked myself out of, due to bad writing. It's just a badly written quest with no real variables and irksome triggers that should lead somewhere, but do not. Heck, involve the Goddessess for a solution, they've not done anything for aeons now.
So, bad advice all around there.