In August 2012, a drug testing laboratory in Boston was closed by the state of Massachusetts. Initial reports simply stated the shutdown was because a chemist working in the lab 'failed to follow testing protocols.' In the months that followed, state officials alleged that the chemist — Annie Dookhan — had not just mishandled criminal evidence but had falsified drug results by deliberately tainting and mixing evidence in tens of thousands of criminal cases. As of this writing, the state has provided what it says is a 'master list' of affected cases, and puts that number at roughly 43,000. However, recent court filings question the accuracy of that number. WBUR didn't want to just follow the latest twists and turns of this story, we wanted to understand how one chemist could cause such a chain reaction that stretched to all corners of the criminal justice system. We wanted to pursue an iterative investigative journalism approach - to show our work mid-process, use data-driven analysis and be transparent about what we didn't know. To date, WBUR is the only news organization to have published an analysis of the testing data.