A judge declared a mistrial Friday after a deadlocked jury failed to deliver a decision in the case of a former Harvard graduate student charged with manslaughter.

The mistrial means Alexander Pring-Wilson will likely be granted a third trial, continuing the four-year legal saga that began when he fatally stabbed an 18-year-old hotel cook outside of a Western Avenue pizzeria in 2003.

Pring-Wilson, 29, said he acted out of self-defense in stabbing Cambridge resident Michael D. Colono, but he was convicted in 2004 of manslaughter.

The Colorado native was sentenced to six to eight years in prison, however, the verdict was thrown out when a higher court ruled that the violent history of the Colono could be admitted as evidence, though it had previously been excluded.

On Friday, the Middlesex district attorney pledged to try Pring-Wilson for a third time, citing several pieces of "compelling" evidence in the case—inconsistent statements Pring-Wilson gave the police, the presence of Colono's blood on Pring-Wilson's clothes, and the fact that the knife used to kill Colono was found in Pring-Wilson's apartment.

"We will honor the memory of Michael Colono by continuing to fight for justice on behalf of him, his family, and the Commonwealth," the statement said.

Pring-Wilson's attorney, E. Peter Parker, could not be reached for comment Friday. He told the Associated Press: "We are thrilled that a number of jurors at this trial saw the commonwealth's case for what it was, and found that Alex's conduct was a justified act of self-defense."

—Staff writer Jamison A. Hill can be reached at jahill@fas.harvard.edu.

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