The victims is male (what a great observation you have, surely the gender should be considered!). He lives in the manor, actually he's the heir of the estate.
There are 8 main characters in the murder mystery and they all have a motive for killing him (think of the board game clue if you've ever played it), so yes he's lived in the manor all his life. He's too cautious to have a personal valet or maid. One more thing, the killer is almost as brilliant as the murderer. He knows he's on everyone's blacklist and that everyone wants to kill him.
The murderer on the other hand, is actually someone that doesn't live in the manor. So there's not much interaction, thus he actually fails to think that the murderer has motive for killing him.
Hope that helps!
The killer is a different person than the murderer? Or did I read that wrong? Or did you mean victim and murderer?
Why too cautious for a valet? If he's heir to a large estate in the late Victorian age a valet would be very commonplace. Getting dressed back then was more cumbersome than today and clothes were changed often during the day at that level of society. Not to mention all the other activities a valet performs that have nothing to do with dressing his master. Who irons his shirts, brushes his clothing and tidys his rooms? He buys his own underwear and socks? Not having a valet would be odd.
The common country activities of an heir to a manor at that time would be
Riding his horse
Driving his carriage
Fishing
Shooting
Hunting
Walks around his property
Meetings with his steward
Meetings with tenants
Church on Sundays
Is he married? If not then he'd have to have meetings with his housekeeper and other staff as well.
You could have the manor be in or near some lovely, rock strewn fishing stream and your murderer happens upon the victim and shoves him down a steep bank strewn with rocks. (Yes, a la
Five Red Herrings, you'd have to work to make it not resonate with Dorothy L. Sayers.) This would work for a murderer not living in the house. Shove him off a bridge into a river? Shove him over a cliff into the sea?
If your murderer doesn't live in the house then he's going to have to kill your victim outside. Carriage wrecks were common. Startle his horses, tip him into a ditch, then bash his head in with a rock? Victim could be known to drive down this isolated bit of road fairly regularly and murderer comes up with an ambush.
Or murderer could happen by when the horses shy and instead of helping the victim straighten the harness and haul the carriage wheel out of the ditch, he bashes him with a rock, drops the rock along side the road and puts victim's head against it. (I'm thinking a curicle or something light, not a coach. He probably wouldn't be driving a coach around the countryside anyway.) Devil of a time proving he did it though unless you have a witness. And a witness would probably report it unless s/he felt it was good riddence and liked the murderer.