In 1916 Dr. Leone Lattes published two cases that illustrated the forensic value of the then new technique for ABO typing bloodstains. Lattes used a method for determining the ABO type of bloodstains that relied on detection of the specific antibodies. Although published 15 years after Landsteiner first described the ABO blood group system in human beings, this work is the first report of ABO typing of dried blood for forensic purposes.
In the first case a man returned home from a trip to another town with what appeared to be bloodstains on his shirt. His wife saw the stains and accused him of adultery during his trip. Though he vehemently denied these accusations, his wife refused to believe him. The man consulted the legal medical institute for help, and Lattes agreed to test the stains to find out whom they might match. The man thought the stains might very well be his own blood, but they could also have been his wife’s or possibly beef blood from the butcher shop. Lattes determined that the stains were human, eliminating the butcher shop possibility, and that they had the same ABO group as the man (type O) but were different from that of his wife (type A). According to Lattes’s account, the findings helped restore peace to this family.
In the second case a man was a suspect in a homicide. He had bloodstains on his coat, but he claimed they were the result of a nosebleed. The suspect was type O, and the victim was type A (determined at the autopsy). The stains were type O, eliminating the victim as a source, and thus exonerating this particular suspect.
Note that because the results of the stains showed a blood type different from that of the victim, the victim could be absolutely eliminated as a possible source. The fact that they had the same blood type as the suspect does not show that they came from the suspect, however, only that they came from someone with blood type O. The results are consistent with the stains having come from the suspect, but they do not prove it by a long stretch. A little less than half the population is type O.
Tests for the ABO antibodies in bloodstains are called Lattes tests. Later, methods were developed to test for the antigens, and Lattes tests became a backup or confirmatory method to determine the blood type in dried bloodstains.