The saga of a former Harvard graduate student charged with manslaughter took another twist on Friday when the judge declared a mistrial after a deadlocked jury failed to deliver a decision.

The mistrial means Alexander Pring-Wilson will likely be granted a third trial, continuing the four-year legal case that began when he fatally stabbed an 18-year-old hotel cook during an altercation 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, but the verdict was thrown out when a higher court ruled that the violent history of 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.

Colono had one daughter, Jade, who was born when he was 15.

Pring-Wilson, who was a masters degree student at the Davis Center for Russian and Eurasian Studies during his time at Harvard, is currently free on a previously-posted $400,000 bail.

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.”

The court will reconvene on Jan. 8 for a hearing to lay out a plan for the third trial.

Originally charged with first-degree murder, Pring-Wilson was convicted of manslaughter in 2004 and sent to prison for five months.

But a ruling on an unrelated case from the Mass. Supreme Judicial Court prompted Superior Court Judge Regina L. Quinlan to grant Pring-Wilson a retrial on the grounds that Colono’s criminal record—which included throwing money in the face of a cashier an shattering the window of a restaurant—could be admitted as evidence, though it was not in the first trial.

The Mass. Supreme Judicial Court upheld the ruling to allow a retrial after an appeal from the prosecution earlier this year.

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

For complete coverage of the Pring-Wilson trial, please see http://www.thecrimson.com/crime.aspx.