I think it's more plausible than the alternative
-
For one thing, why was he armed in the first place? Why did he have enough weed to keep the apartment building stoned for five years? If it was planted, how did the cops prevent anyone from seeing them plant it? Why haven't the men implicated the cops? How do I prove a negative?
On the weight of the evidence, it either was a drug deal gone wrong or it was a hit by the cops. One piece of speculative evidence, the timing, suggests it was a hit. Every other piece of evidence suggests a drug deal.