I'm not sure if this is the case. Turvey said in his examination that MM had no abrasions, while CB and SB had 'deep ligature furrows with ligature abrasions'. According to the autopsy report, all three victims had binding abrasions. Where did you hear that CB had little to no bruising around the bindings?
Injuries of Right Arm:
Scattered abrasions were present over the right arm and forearm. A yellow binding abrasion which was not surrounded by contusion was present on the right wrist.
Injuries of Left Arm:
Multiple scattered abrasions are present on the anteroposterior surfaces of the left arm. A binding abrasion was present on the left wrist and at the superior margin of this abrasion was a faint red-purple contusion.
http://callahan.8k.com/wm3/autsb.html
Compare it to the other autopsy reports on Callahans (snippets below), and you'll see that the abrasions surrounding the bindings are much more defined and darker than CB's (yellow, faint red), which would indicate his heart all but stopped pumping blood before he was tied.
No offense, but I don't really know where you are getting your information, when you say that Turvey said MM had no abrasions, when it clearly states otherwise here:
MM:
Upper Extremity Injuries:
The wrists showed binding abrasions. Situated around these abrasions were contusions.
Situated on the left antecubital fossa was 1/8 inch abrasion. Below this were linear abrasions measuring from 1/16 inch to 1/2 inch.
SB:
Upper Extremity Injuries:
On the back of the hands were multiple scattered contusions. Scattered contusions were also present on the thenar eminence bilaterally.
Binding abrasions with surrounding red contusion were present on the wrists.
Can you link me to where you're getting your info?