Or, how about you see who is responsible and it is a powerful political figure? Do you want to try to convince the authorities he did it and to do something about it? Will that just put you in danger? Will the knowledge alone put your life in jeopardy?
Exactly -- knowing who did it and proving it are entirely two different things.
As has been pointed out before, the word of a single caster is not going hold a lot of weight if there is no proof, it comes down to caster's word versus culprit's word.
And as has also been pointed out,
IF the use of such spells are a common practice, then the opposition (thieve's guild, assassin's guild, etc)
ARE going to come up with counter measures that prevent its use or misdirect things.
Additionally, there is "plausible deniability".
I remember hearing or reading about this English (I think) ruler who, instead of saying "I want him dead" said something along the lines of "My life would be easier without him" and one of his courtiers decided that the King wanted him dead and so had him killed.
Now suppose a person in power says "I wish he wasn't such a thorn in my side" and was only ruminating out loud with no ulterior motive (i.e. did NOT want "him" dead) and some retainer takes it the wrong way and has "him" killed. Who is ultimately responsible there? The guy who misunderstood his bosses wishes or the boss.
By the wording of the spell, the boss would be ultimately responsible because his words were what put into motion the chain of events that caused the death, but he would also be innocent at the same time because he didn't really want the guy killed.
And most important thing to remember is that the spell only gives visions, it does NOT give names or any other information. So, if the caster had never seen or met Durgan One Eye, the spell showing an image of him would do no good in catching the killer.