The scientists collected genetic samples from men infected during the late 1970s, and used RNA "jackhammering" to break apart the subjects' HIV genomes and recombine them into usable RNA sequences. From there, the team used known mutation rates to determine the sequences' common ancestor. Simply speaking, there was too much genetic diversity by the late 1970s for Patient 0 to be responsible -- HIV had to have arrived earlier.
The findings may well clear the attendant's name, but they should have a longer-lasting impact on our understanding of disease as a whole. The approach could help humanity understand how viruses spread and track their evolution. It won't directly contribute to possible cures, but following the development of a disease might help illustrate the seriousness of a given threat.