The state's highest court ordered a new trial yesterday for a man convicted of killing two relatives and wounding another during a family dispute.
John Hinds was convicted of wounding his sister and killing his half-brother and his half-brother's wife in October 1998 on a residential street in Cambridge.
Prosecutors portrayed Hinds as a self-absorbed person who had a deliberate and premeditated plan to kill his relatives so he could gain control of his elderly mother's house.
The state Supreme Judicial Court overturned his conviction, agreeing with Hinds's lawyer that the judge at his trial gave faulty instructions to jurors on how they should evaluate expert testimony from a defense psychiatrist.
The psychiatrist asserted Hinds was mentally impaired at the time of the shootings and did not have the capacity to premeditate or intend to kill anyone.
The SJC found that the judge's instructions incorrectly indicated that the jury should disregard the psychiatrist's testimony unless it was based on facts prosecutors had proved beyond a reasonable doubt.
"The instruction, essentially, eviscerated any value to the defense of [the psychiatrist's] testimony," the court said.
Myles Jacobson, the lawyer who represented Hinds in his appeal, said the judge's instruction was particularly damaging because Hinds's entire defense was based on a claim of mental impairment.
A message left at the office of Middlesex District Attorney Gerard T. Leone Jr. was not immediately returned yesterday.
Hinds has been in prison since his arrest shortly after the shootings.