The shoe was allowed to stand for 35 minutes to allow complete soaking of the blood into the leather and complete drying, which actually required a very short time. The shoe was then immersed in water and forced back and forth in the water to simulate the washing action of water movement for five minutes, after which some of the spots had disappeared and all reduced in size, but 16 spots could still be observed with the eye. Because the treatment did not apply mechanical action to remove the blood spots as would walking, the wet spots were rubbed vigorously with paper toweling until no actual spots could be seen as such. The shoe was then returned to fresh water for five more minutes, after which it was removed and allowed to dry.
Inspection with magnification revealed that blood was still visible in three places, twice where it had soaked into the stitching; the largest visible quantity was in a small cut in the sole of the shoe.
This experiment shows that blood adheres to surfaces into which it can soak with considerable tenacity as previously shown with clothing and in contrast to the behavior on smooth, non-absorptive surfaces such as metal watch bands. It is very probable that even the visible blood would have disappeared with walking, but certainly not to a point at which chemical blood test methods would not have revealed its original presence.
Paul L. Kirk investigation, forensic testing, Wash-off Experiments