Prove the original crime, don’t rely and peripheral procedure like “they lied to a federal agent” (uhh) cop-out. Do your job.
Likewise I’m not don’t of people getting off on “technicalities” (Some more than others)
Presumably there's some level of incentive to catch criminals. Otherwise why would police officers do anything? (Of course another possible answer is that they don't).
> If so, why couldn't we just keep that part and not release the criminals on the technicality?
Because it's very hard to maintain an incentive unless it's aligned all the way through an organisation. The consequences for police dishonesty needs to be something that will cause police chiefs to lose elections. Letting criminals go free is one of the few things that does that.