Gabriel Okeynan, who was 45, was found with stab wounds just before midnight on June 20 outside Marlborough Mall.
He died on Tuesday.
A 16-year-old boy also faces charges of robbery and second-degree murder.
Staff Sgt. Colin Chisholm told reporters earlier this week the attack appeared to be random, and the victim was alone.
Neither teen can be named because of their ages.
Police are not looking for any other suspects in the case.
“We have no information to believe that the victim and the offenders had any previous relationship,” he said.
Police are asking anyone who might have witnessed the attack or has information about the case to call them or Crime Stoppers.
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