In 2003, Thompson won a $14 million award from a federal jury that concluded Connick had acted with "deliberate indifference" by failing to train his underlings in their constitutional obligations. An appeals court upheld that award in 2008.
It's hard to say which would be more appalling: if prosecutors intentionally hid the blood test, or if they did not know they were required to share it. There is evidence to support both theories.
In 1994, after he was diagnosed with terminal cancer, one prosecutor told a former colleague (who kept this information to himself for five years) that he had deliberately withheld the blood evidence. But it's not clear he knew that was illegal at the time of Thompson's robbery trial, and testimony in Thompson's civil case indicated that other prosecutors in the D.A.'s office, including Connick himself, did not know they were legally required to share the crime lab report.
Thompson's lawyers note that one prosecutor's "misunderstanding" of the relevant Supreme Court ruling "was so fundamental that the district judge visibly registered surprise," prompting him to change his testimony.
The Supreme Court has ruled that local governments can be held liable for failing to train officials in their constitutional responsibilities when the need is "obvious," as with teaching police officers the proper use of deadly force. The need for prosecutors to respect defendants' due process rights is no less obvious. And since prosecutors themselves have absolute immunity for their trial-related misconduct, the threat of lawsuits against their employers is an important safeguard to prevent the pursuit of victory from trumping the pursuit of justice.