"Tell you what Buttercup"
During law school Betty Anne Waters is desparately trying to think of ways of helping her brother, Kenny, prove his innocence. When we watch the film it all so seems so flimsy, that his blood group, "O", was found at the scene. One of the most common blood groups around but sufficient to convict. (Strains of Rumpole's rhapsody on blood stains in the Penge Bungalow murders....)
At the time of Waters' trial DNA testing didn't really exist so the blood at the crime scene wasn't tested. (If you're unsure about what it is watch any episode of CSI or CSI Miami.
Betty Anne contacts the Innocence Project in New York for help. She receives a positive response provided she can locate the blood samples used and that she is prepared to wait 18 months because of the backlog of cases.
The Innocence Project was founded in 1992 by Barry Scheck and Peter Nuefeld to assist prisoners who could be helped by DNA testing. Both Scheck and Neufeld were counsel on O.J. Simpson's defence team. The project has now gone international and has members in the UK, Canada, Australia and New Zealand.
Locating the evidence in Kenny's case becomes a central feature of the film. Betty Anne receives no help from the police or the court where the evidence was supposed to have been stored. Eventually she finds a helpful custodian who searches and locates the boxed evidence including the blood samples. Independent lab reports exonerate Kenny.
Without the assistance of the Innocence Project Betty Anne wouldn't have been able to help her brother. The film portrays Scheck (Peter Gallagher) accompanying her around Massachusetts as they look for witnesses. Despite the obstacles thrown up against them by the police, the DA, and the system, they succeed.
You can read the case file on Kenny Waters at the Innocence Project. There are original documents from the case as well as interviews with Betty Anne.
It's worth noting that recently doubts about the efficacy of DNA testing have begun to arise. Can DNA become contaminated? Can the evidence be faked? See this article on the faking of DNA. In the UK it has arisen in connection with case of James Hanratty who was hanged in 1962 for murder. The UK Innocence Project, called Innocent, has been trying to show his innocence. But it isn't clear whether the DNA evidence is conclusive or not.
Which reminds me of one line in the film. Someone says it's fortunate that Massachusetts didn't have the death penalty or Kenny wouldn't be around to appeal.