They might have more interest in planting incriminating evidence on someone - whether a random person or the actual suspect, if the cops don't find anything on them - if it's part of an inter-agency investigation.
this hypothetical scenario has nothing to do with parallel construction. the DEA could plant incriminating evidence on a random person and the results would be the same.
Your missing the point that a tip handed down tip from NSA has authority. It must be right, right? Thus in stilling idea that target must be guilty. And if they get off it's your fault. This leads to all manor of things from unconsciously triggering drug dog, to forced enemas, to planting evidence.
This happens. All the time. It is not theoretical. Innocent people are dead.
I am not willing to trade innocent life for the theoretical "more safety" promised.
Ideally they wouldn't have to as after they apprehend the people they would find drugs on them.
The main idea is that they need an plausible explanation to the court and the outside world on how they got the evidence.
Not justifying or saying I like what they do, just explaining how I understand parallel construction to work.