fred hrusa. he identified the usual specimens you would expect to find underneath a car, grass, dirt, debris. but he also found large quantities of yellow starthistle, a weed. >> i saw the yellow starthistle and then i saw the small scraps that had been taken off the body. and i was able to compare that to the material that had been collected from the area around the body and also from the trees that were in the overstory above the canyon where the body was found. >> dr. hrusa was looking for what botanists call diagnostic characteristics, unique aspects of the plant that differentiated from others of the same species. dr. hrusa discovered the starthistle under doug mouser's car was identical in development to the starthistle found near genna's body. while this was significant, it wasn't enough to tie doug mouser to the murder. >> the yellow starthistle is not a rare plant. it is an extremely common plant. so in any given area of -- especially of northern california, and at low elevations, yellow