“Over the following years, Lattes, and a growing band of fellow forensic serologists, were called in to use both the precipitin test and blood grouping in an increasing number of cases. Although they acknowledged that they were nowhere near being able to tell whether a bloodstain came from a particular person- the groupings were far too large for that- and it was of no help if the victim and suspect shared the same blood type, the techniques proved to be powerful in excluding suspects, narrowing down the list of potential culprits, and above all, as tools to produce a confession” (Weinberg 53)
The discovery of the precipitin test started a trend of forensic discoveries. But each of these tools that scientists uncovered proved to be useful only in eliminating suspects, not finding guilt. Like Weinberg said “the techniques proved to be powerful in excluding suspects”. Not until the ability to profile DNA was discovered were scientists able to prove guilt of a suspect. This perhaps is why the detectives in the case of Helena and Mr. Frediani were forced to question him instead of just simply arresting him. They could prove that he was indeed on the scene but not that he committed the crime. They were using the tools that were covered in the chapter like the precipitin test to exclude other suspects and use them to “produce a confession” from Mr. Frediani.