Having all the incriminating evidence on him seems... Extremely unlikely considering the rest of what we know about the situation.

That's the type of shit you'd expect from desperate police planting evidence. Planting a random suppressor, a supposedly "phantom" 3d printed gun, and a manifesto isn't exactly hard. Only the gun could possibly be directly traced to the bullets fired, and that's not something they can test in the field.

Not saying that's necessarily the case here, but this would not be the first time law enforcement, including the FBI, planted evidence because of outside pressures.