It's fairly obvious that she committed every one of those murders...

She had the means (bored millionaire supergenius) and the motive (testing the viability of plots for her novels) to off dozens of people in short order. We are supposed to believe that all those suspicious deaths just happened to occur in proximity to the same little old lady over and over again. To think of all the innocent people she gleefully sent to the chair. O, Jessica Fletcher, you bike-riding angel of death. You'll get yours.

Let's see who takes the bait.