Have you looked at the bath mat?
http://themurderofmeredithkercher.com/The_Bathmat_Footprint
http://amandaknoxcase.com/wp-content/uploads/2014/04/13.jpg
http://amandaknoxcase.com/wp-content/uploads/2014/01/page26.jpg
Note how the bath mat has an irregular surface partly flock and partly smooth. The heal is not on the absorbent surface of the mat, it is off the edge. The pictures of the mat in situ show the presence of the heal on the adjacent tile. So first error in your assumptions; the heal print is present and was not removed.
Look at the pictures yourself, then admit that you are wrong in your claim the heal print was cleaned away.
We can note this was dilute blood, there are no 'clots' on the surface as we would see with fresh blood, this was dilute blood that soaked into the mat.
The police 'experts' who examined this were fingerprint specialists. The appropriate experts for examining footprints are forensic anthropologists or forensic podiatrists. When asked about whether he considered the shape of the footprint Lorenzo he relied ‘we didn’t consider it … because I hold that it requires knowledge of orthopedics’. Exactly if you do not have knowledge about anatomy of the foot you are not an expert of footprints.
The sad thing is the footprint analysis is the clearest example of malfeasance as the figures to prove it are given.
The standard footprint is taken standing with a viscous ink (does not run), on a firm non-absorbent surface. No print would be expected to be identical, footprints vary in size from morning to evening by 3 - 5mm depending on parameter, by a similar movement comparing a static stand with a dynamic step. Repeated prints at the same time on the same surface will vary +/- 1mm. A good example of this is the measurement of the same dimensions on the well defined sample print of Sollecito is not identical between Vinci and the Scientific Police. (Also of note Vinci found hairs on the bath mat not noticed by the scientific police).
A priori a footprint by stepping on an absorbent, yielding (will wrap round the foot), surface with a runny (dilute fluid) would be expected to give a larger print than the standard print. The bath mat print was deposited at the end of the day and should be bigger than the standard print taken during the day. The bath mat print has no clear edge.
So what results do the police 'experts' get?
http://www.internationalskeptics.com/forums/attachment.php?attachmentid=34277&d=1450198223
50% of measurements are identical. This is just impossible.
But the key measure is the length of the ball of the foot. This is measured as being 50 mm on the bath mat vs. 57mm for Sollecito. If the other measures are mm accurate then this measure MUST exclude Sollecito as the source. One cannot argue that this measure is inaccurate because if one tries to extend this dimension on the bath mat to match Sollecito then most other measures are affected and then increase by 5+ mm and no longer match Sollecito.
It cannot be emphasized too much. The prosecution ‘expert’ was a paid consultant a fingerprint expert with no expertise in footprints a very different issue.