Defamatory? What part of "based" on a true story do these guys not understand? First of all, 99% of everything based on a true story is complete BS. Secondly, they do that to protect themselves from lawsuits such as this. 😉
If you've ever seen a police procedural on TV, you're probably familiar with the technique -- it's the one that verges on a "good cop / bad cop" approach in which a good cop tries to "justify" the crime, telling a suspect all the reasons why it's "understandable" why a person would have committed the crime.