UPDATE: Reactions from the DA's office and the victim's family in the comments below.
The Supreme Judicial Court today ordered a new trial for Lamory Gray, ruling the Heath Street gang member got an unfair trial before he was convicted of murdering somebody he thought was a member of the rival H-Block gang  in 2006.
The court ruled a rap video, in which Gray was seen apparently pledging as a member of Heath Street, should not have been entered as evidence in his 2009 trial because it unfairly prejudiced the jury against him without having any direct connection to Herman Taylor's murder. Taylor was a Metco student who had nothing to do with gangs.
The judge in the case at first rejected a prosecution request to show the video, but relented when Gray's lawyer appeared to contest the assertion that Gray was a member of the gang.
The state's highest court called that a mistake. Prosecutors had other, less prejudicial evidence that Gray was a Heath Street member at the height of its bloody feud with H-Block - he had an entry in a BPD gang database, for example.
And, the court said, simply participating in a rap video doesn't mean one is admitting to anything - since rap is a form of artistic expression. It's past time, the court said, to give rap artists the same due as people such as Johnny Cash, who sang about shooting a man to watch him die, and Bob Marley, who sang he shot the sheriff, even though neither actually did so:
We discern no reason why rap music lyrics, unlike any other musical form, should be singled out and viewed sui generis as literal statements of fact or intent.
The court added the BPD detective who explained the video to the judge might be an expert in gangs, but he failed to provide any bona fides for analyzing rap music:
Although [a BPD detective] asserted during [a court hearing] that the video "consists of discussing being a Heath Street gang member and what takes place or what's done or conducted by individuals who are Heath Street gang members," there was no evidence that Sheehan was an expert on music video recordings or rap music. A police officer who has been qualified as a "gang expert" cannot, without more, be deemed an expert qualified to interpret the meaning of rap music lyrics.