In unbreakable why doesn't David "sense" that Elijah planned the disasters sooner?

I know that David sensed what Elijah did at the end when they shake hands but why did it take him so long?

I think I recall he "sensed" that the man in the army jacket had a gun in his belt without coming into contact with him and while he was a good distance away from him. Why didn't he sense what Elijah had did?

Is it because his ability to see things increased throughout the movie?