It was one of the more curious developments in a case that has had many twists and turns: Photos obtained by the widow of Bob Cassilly this summer show what appears to be a bloody patch, and a rock, near the bulldozer where his body was found.The founder of the City Museum, Cassilly died five years ago in what the St. Louis medical examiner quickly labeled a bulldozer accident. But his widow Giovanna has been seeking to persuade authorities to reopen the case, arguing that a cursory investigation on the part of law enforcement missed clear evidence that he was murdered.…