A few hours? And no one noticed in all that time.

[He figures they can check the body to confirm just how long ago it was, too, if no one else has taken note of that.]

I agree, it was very likely purposeful. It may have been an attempt to make it look like an accident-- one might assume he tripped during a late-night walk, I suppose, unless he has other wounds as well. But I'd think a wound to the head involving this much blood could certainly kill someone by itself.