BOSTON -- A former Harvard University graduate student pleaded guilty to involuntary manslaughter in Cambridge Superior Court on Friday in the stabbing death of a teenager who made fun of him.

Alexander Pring-Wilson has already been tried twice in the stabbing death of Michael Colono, 18, during an April 12, 2003, street fight.

Pring-Wilson, 29, avoids a third trial by entering the plea as part of an agreement with prosecutors. He's expected to be sentenced to two years in prison for Colono's death.

"At the end of the day, the measure of justice is the fact that Alexander Pring-Wilson can no longer profess his innocence. He has admitted his guilt, and he is a convicted killer," said Middlesex County District Attorney Gerry Leone.

A family friend told TheBostonChannel.com's sister Web site, TheDenverChannel.com/KMGH-TV, that by pleading guilty, Pring-Wilson avoided a seven-year prison sentence if convicted in a third trial. Although he is expected to be sentenced to two years in prison, a family friend told TheDenverChannel.com that he could be out in as little as 11 months, after credit for time served in jail.

Leone said Pring-Wilson will serve at least one full year in prison.

A guilty plea to involuntary manslaughter is not the ending Colono's family wanted.

"We have been robbed of what is natural, of what is right and what is justice. We, the Colono family, do not know how to continue on with life since Michael was killed," Colono's sister, Desmarias Colono, said.

"Overwhelming sadness and anguish do not leave my side -- not even for a moment," Colono's sister, Juanda Rivera, said.

Pring-Wilson, a Colorado Springs, Colo., native who was studying for his master's at Harvard's Davis Center for Russian and Eurasian Studies, was originally charged with murder in Colono's death, but a jury convicted him on a lesser charge of manslaughter in 2004. In June 2005, that conviction was overturned after his attorney successfully argued that evidence of the victim's violent past should have been allowed at trial.

At the time of the fight, Colono, a father and a cook at a Boston hotel, was on probation on charges of drug possession and malicious destruction of property.

After 10 days of deliberations in Pring-Wilson's second trial in December, a Middlesex Superior Court jury said they could not reach a verdict and that case ended in a mistrial.

Arguing in both trials that the stabbing was in self-defense, Pring-Wilson's attorney said Colono was the aggressor and teamed up with his cousin to beat Pring-Wilson to the ground on a Cambridge street.

After the December mistrial, prosecutors immediately said they would try Pring-Wilson for a third time.

"The one thing we have never forgotten is Michael. We speak for people with no voice. And each and every day that this case went by over the course of the last four years, we never forgot Michael," Leone said.

Pring-Wilson's mother is a former deputy district attorney in Colorado Springs and his father is a criminal defense lawyer.