See: http://prawfsblawg.blogs.com/
Causation Anonymity in Group Police Misconduct: No Conviction, No Justice, No Peace
"And therein lies the rub. This decision paves the way for causation anonymity to immunize homicide, any time a group of police officers (or gang members or any other shooters) act together to end another human being's life. We can never know which bullet caused death. We therefore can never know which shooter caused death (at least from a legal standpoint). And we can never, therefore, punish the murderer."