One of the myths surrounding the evidence in this case is that Rudy Guede's foot is too big to have made the print on the bathmat, but Raffaele's foot is the right size. This is simply not true.

In fact, Rudy's reference footprint is longer overall than Raffaele's, but the forefoot region is neither longer nor wider. This part of Rudy's foot is actually a little smaller than Raffaele's. Moreover, the reference prints for both Raffaele and Rudy are longer in the forefoot region than the print on the bathmat.
It is not certain how the footprint was made, but evidence suggests the killer cleaned up in the bathroom, and several blood-soaked towels were found at the crime scene. Very likely the killer laid a bloodied towel on the bathroom floor so that it covered or overlapped the mat. He removed his shoe to rinse the blood from it. While his shoe was off, he stepped on the towel, transferring an imprint to the bathmat.

The outline of the foot is incomplete. The heel extends off the edge of the mat, and parts appear to be missing in the upper right and lower left quadrants. Under the scenario described above, these missing elements can be explained as areas where the towel was dry or where the foot extended beyond the edge of the towel.

The photo below shows a close up of a partial bloody bare footprint found on the bathmat in the bathroom. The prosecution went to great lengths to show that this bare footprint was made by Raffaele Sollecito.
The photo below shows the bathmat in the bathroom. You can see the bare foot print, set in blood, on the bottom left corner of the bathmat.
The critical error in Lorenzo Rinaldi's measurements
Lorenzo Rinaldi is the director of the print identity department of the Italian Police The myth about the size of Rudy's foot is largely the result of the report that Lorenzo Rinaldi presented in court.

Proper inspection of the bathmat clearly shows that the tip of the second toe blended with the top of the big toe. Rinaldi measured  the big toe including the top of the second toe. This error caused the width of the toe to measure 30mm. Rinaldi did not observe that the second toe had blended in with the big toe on the bathmat. The nature of the absorbent carpet may have lead to natural spreading of blood.  This print was made is bloody water, not pure blood. This would have attributed to the spreading of the liquid as it was absorbed into the rug. This error in measurement is crucial because the prosecution based the compatibility of Raffaele’s foot on the width of his big toe.

Raffaele’s big toe measured 30mm and is therefore incompatible with the measured foot on the bathmat. When measured correctly, the print on the bathmat measured 24.8mm. 

It is impossible that Raffaele’s foot made the print on the bathmat.

The photo below details the area of the print that was measured incorrectly by Rinaldi. The small circular spot is actually an imprint from the second toe. Rinaldi's measurement of the big toe incorrectly included the imprint of the second toe.
As you can see from the sample prints below,  the actual measurements are similar to Rudy's footprint. There is absolutely no way the print belongs to Raffaele. The photos below are not to scale with the bathmat image. They are posted here to observe the different characteristics and to point out the obvious error in measurement by Rinaldi.
Rudy's footprint
Raffaele's footprint
Injustice in Perugia
a website detailing the wrongful conviction of Amanda Knox & Raffaele Sollecito
The Truth About the Bare Footprint on the Bathmat
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Raffaele Sollecito's forensics expert Francesco Vinci clearly showed that the bathmat print did not match Raffaele's foot. A few pages of his report are shown below. You can view Professor Vinci's entire report here.