FAIRFAX, Va. -- A 15-year-old boy who killed a clerk while robbing a Mount Vernon 7-Eleven has been sentenced to stay in juvenile detention until he turns 21.

Rody Phillips also was sentenced to 25 years in prison after he turns 21, but that part of the sentence was suspended.

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Phillips was charged with first-degree murder and attempted robbery in the death of 60-year-old Sun Koo Kwan on Dec. 6, 2004.

The teen apologized for the crime Friday, and his mother offered her own emotional apology, News4's Michael Flynn reported.

"To Mr. Kwan's friends and family I'm sorry that this ever happened," Stephanie Waters said. "Not only is Mr. Kwan gone, but my son's childhood innocence is gone because of all this."

In court, Phillips was unemotional as he apologized for the crime.

His family said he was having emotional problems before the attack. A doctor prescribed him the antidepressant Effexor, which his defense attorney said is not approved for adolescents and led to Phillips hearing voices. His family blames the drug for his violent attack.

"I don't place all the blame on Effexor," said prosecutor Ray Morrow. "I think, unfortunately, this was a troubled young man, and there were a number of issues at work."

With good behavior, Phillips will be able to go free when he's 21.

"We've asked for and got something that is fair," said Phillips stepfather, John Waters. "He will be punished for what he's done, but we can still help get him the help he needs so he can be a productive person for society."

The teen's family members said they'll never forget the innocent life their son took.

"For a man I never met, he will always be a part of my life," Stephanie Waters said. "I'm sorry that he's taken away from his friends and his family, and my son's tremendously sorry, also."

A spokesperson for the company that produces Effexor said the drug is not FDA approved for use in youngsters but said it has helped millions of adults battle depression.

Phillips' victim was just a few years from retiring as a clerk and was planning to move back to Korea to be with his family.