According to the rules of Wonderland,
basically,
Gabriel Hawkins can detect any killing intent directed at him from any distance,
however,
since he is a vessel for a dark entity, this entity can sense other entities and may or may not warn him, (I will disregard it as it is not guaranteed.)
but he also has a sixth sense, but it only works in a direct line of sight with the trigger,
when this happens,
Gabriel will feel an unnatural fear, the amount of fear increases with the threat level of the trigger,
he can overcome this fear, but sometimes, there is no point in doing so.
With that in mind, I have to assume that Gabriel Hawkins wouldn't sense him ONLY if he posed no threat to us, which, to me, is impossible to believe.