One of the reasons you should almost never cooperate with the police is because they might force you to testify against someone who has committed a victimless or deminimis crime.

Which could put you in the position of aiding in the unjust punishment of someone. Legal penalties today are so disproportionate that unless there is real physical violence involved people who "cooperate" are at risk of doing much greater harm than they prevent.

So save yourself some grief. Just don't talk to them.