she's annie dukan, a former chemist, helping police by analysing evidence for the preps of drugs. >> reporter: what goes through your mind when you hear the name annie dukin? >> a lot of good hard work by a lot of people was thrown out the window. >> reporter: her job was to identify and weigh parcels of heroin or cocaine. for 10 years she did her job. the star chemist not only lied about her credentials, she tampered with the drugs. court records showed thee handled samples without supervision, intentionally contaminating them. sometimes she eyeballed them guessing, instead of testing them. >> reporter: the day the prosecutor learnt convictions in his country were tainted. >> i knew we had a problem. the drug cases were serious cases with violent criminals. i was right to be worried. i have an obligation, as do other das, to make sure convictions are based on good, solid evidence, and that this does not taint our convictions. >> all these files are dukin cases. this filing cabinet is dukin cases. >> every is a person, file or case to do with dukin. >> yes. and these are just distric