they have to have more than one eyewitness to convict for petty posession/trafficking (small amounts) and they have to be able to prove it was marijuana. A police officer cannot get a conviction if the "offender" was "pushing" a bag of fucking oregano.

And as for admitting what you did? Screw that. Only say "I want to speak with my lawyer." and listen to him/her. Most convictions for drug trafficking come from admissions/deals... Just don't say a word except to your attorney.