> If a cop asks if you want to buy some drugs and you say yes then the cop can be punished, not you, no matter if you might be suspected of wanting to buy drugs.

In this engineer's case, this is more like the engineer being a well-known drug dealer and the cop asking if the engineer can sell the cop drugs, then the engineer (willingly!) giving the cop some drugs and the cop then arresting the engineer. You have it backwards here.