A federal judge overturned the death sentence of a man convicted of killing 13 people in the 1983 "Chinatown Massacre."

U.S. District Judge William Dwyer ruled Tuesday that Kwan Fai Mak's lawyers didn't present testimony on Mak's background as a Hong Kong immigrant or other evidence that could have swayed the jury to spare his life.King County Prosecutor Norm Maleng said he'd decide in a week whether to appeal.

Mak, 30, and Benjamin Ng were convicted of 13 counts of aggravated first-degree murder in a February 1983 robbery at the Wah Mee gambling club. Mak was accused of masterminding the robbery in which 14 people were bound and shot in the head. One elderly victim survived and testified at the trial.

Ng had his mother testify and was sentenced to life in prison without parole.