Since a few decades ago, DNA testing became an important tool in criminal forensics, and a lot of information can be gathered from a single drop of blood or from a few cells.
Even before that, blood type could be used even in the early 20th century, to at least exclude 3/4 of possible suspects.
However, when did it first became possible to distinguish between human and animal blood, and what method did they use? Is there information about the first time it was used
as evidence in a trial for forensic purposes?
I would suspect it was not sooner, or not much sooner as the discovery of the ABO blood types at the beginning of the 20th century. There are modern, much more accurate methods, and the introductory parts of such papers likely mention the early history, but they are behind paywalls.