The identification of an individual's fingerprint in the blood of a victim of crime is extremely powerful evidence. However, there's very little published literature on the various factors that affect the appearance of a fingerprint with the interaction of blood.
One published technical report states that it's not possible to determine how a fingerprint has interacted with blood just from its appearance. Some fingerprint experts are prepared to comment on how a fingerprint has been formed, while others will only comment on the identification.
From previous experience, authentication of a fingerprint associated with blood should be a joint examination by a fingerprint expert and a forensic scientist. The scientist would consider the interaction and distribution of blood on the surface of the object and the fingerprint expert would look at the interaction of blood with the ridges and furrows of the fingerprint. This paper demonstrates that by analyzing the mark of a fingerprint, the scientist would be able to determine if:
- The finger was wet with blood when it made contact with the object
- A clean finger made contact with blood that was already on the object
- Blood has come into contact with an existing finger mark on the object
There may be other explanations such as combinations of the three above. However, in the author's experience these are the most common explanations.