Advance readers were quite sanguine about the underlying bogus science, but were unconvinced by the Damascene conversion of the cop from cynic through agnosticism to convert over a period of a few hours. There was also the usual problem with fictional cops - if they're senior enough to make decisions, they're too senior to actually do any investigating and vice versa.
It should be fairly easy to have a lieutenant assign detectives to investigate the kid's claims. Once they have, confirming his information, the lieutenant could then act on the information. It also shouldn't be hard to extend the detectives skepticism for a couple cases ("Ya just got lucky, kid. Don't think it proves anything!")
The more difficult problem would be getting the cops to take such claims (I can tell you who did it) seriously without something to substantiate his claim (something psychics face all the time, though a few have managed it--mostly when the police are desperate for leads to stale investigations).
A fun alternative would be to have the kid (I'm assuming he's young) tell the kids he knows who did it, only to be chased out of the office. He later phones the cops about a lead, and when they show up, he's already captured the criminal with the evidence (following a bumbling confrontation), though it'll be difficult to keep it realistic given the tendency of non-cops to screw up evidence (and not to know the difference).
Magical devices are difficult without a somewhat realistic rational for how it works. If it's alien, then you'll need to explain how the protagonist came across it, and the explanation of either needs to be decent, as the entire story rests on readers accepting it.
Instead of a device, I'd go with a newly blossomed psychic ability. It's the easiest to deal with. If he only has partial visions, leaving him unsure of the details, ratchets up the tension. After that, he'll have the duplicate challenges of hiding his secret, and figuring out where the abilities come from, and what it ultimately means (throw in govt. agents, spies or bad guy syndicates however you desire).
If you don't fell comfortable writing it, then consider what I've said, and see whether a suitable plot alternative will build over time. Chances are, you'll think of a suitable resolution in a fairly short time.