"It is not always evident whether the blood portion of a bloody friction ridge impression represents the ridges or the furrows of the skin surface. If the skin makes light contact with a source of wet blood (or other serous fluid) so that only the ridges are coated with blood, the bloody areas of the impression resulting from a subsequent touching of some object represents the ridges on the original finger. On the other hand, if the quantity of blood on the friction ridge surface is sufficient to fill the valleys between ridges, then the bloody lines in the subsequent impression produced may be caused by the blood in the furrows between ridges. In general, it is not possible to distinguish between these two circumstances by examination of the impression.
The amount and condition of the blood transferred to a finger is dependent on the nature of the source of the blood, and the details of the contact between the blood and the friction ridge skin. The scene photographs show at least four areas with significant blood pools: two on the bed and two on the floor. There may have been other pools of blood on the decedent's body or clothing. If these pools of blood were still liquid when they were touched by Mr Hillstead, the amount of blood that transferred to his hands could have been sufficient to produce the fingerprints depicted in the photographs supplied.
The critical issue in this case is the condition of the blood that Mr Hillstead touched. It is difficult, if not impossible, to determine if blood was present several hours after the initial assault that could have transferred to Mr Hillstead's hands, or if such blood would only have been present a few minutes after the original assault. Environmental variables (temperature, humidity, air movement), the location of the blood which may enhance or impede the drying process, the amount of blood present in a pool or other location that Mr Hillstead may have touched, and the manner in which any contact occurred are among the factors that might have influenced the nature of the blood on his hands.
Further, the time between the contact with the source of the blood and the production of the bloody impression, and the amount and condition of the blood transferred to the skin, will affect the appearance of the impression. Dry blood on the ridge surfaces may adhere to the skin while wetter blood in the intervening furrows will be transferred to the contact surface leaving a negative impression. Alternatively, a thin coating of blood which is only on the surface may still be moist enough to transfer to the contact surface leaving a ridge impression. Another possibility is that wet blood on the skin surface may be forced into the furrows resulting in a negative impression."