[rdtsc]

Well planting incriminating evidence is a separate problem. They can do that with or without parallel construction.

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.

[Semiapies]

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.