The man who authorities have charged with fatally shooting Rebecca Payne in her Boston apartment four years ago has been described as a career criminal.

Cornell Smith, now 30, of Boston, was revealed to have a long history of substance abuse when he was sentenced to federal prison for a drug sale that occurred three months after the New Milford woman was killed.

He is currently serving a 12-year term for distribution of cocaine, a sentence imposed by a federal judge in January 2010, according to court records.

Ms. Payne, a 22-year-old student at Northeastern University, was killed on May 20, 2008.

Mr. Smith has been incarcerated since Aug. 16 of that year, after officers from an anti-drug unit observed him selling $80 worth of crack cocaine to a customer on a Boston street, according to the arrest warrant affidavit that is part of the court file.

A Suffolk County grand jury on April 27 indicted Mr. Smith and another man, 55-year-old Michael Balba of Billerica, Mass., in connection with Ms. Payne's death.

Mr. Smith was charged with the murder, and Mr. Balba was accused of lying to the grand jury, which authorities said hampered the work of investigators and delayed solving the case.

Suffolk District Attorney Daniel Conley said Ms. Payne, whose parents still live in New Milford, was an "innocent victim" and had no connection to either of the men.

Some media outlets in Boston have said she was a victim of mistaken identity, but the district attorney's office refused to comment on those reports last week.

"As prosecutors, we're never obliged to prove motive, and at this point we aren't going to discuss potential reasons Rebecca may have been killed," spokesman Jake Warke said.

At the time he allegedly shot Ms. Payne, Mr. Smith was free on bail after being charged for a drug sale in February 2008, federal court documents indicate.

Although Mr. Smith hadn't been charged with selling a large quantity of crack in the case last August, Judge William Young said, because of his lengthy criminal record, the 12-year term was justified under federal sentencing guidelines.

"Mr. Smith is a career offender," the judge said. "When you re-offend, and re-offend again, and then re-offend after that, the reaction of the courts, any court, is `Well, that didn't work, now we'll give him longer time.' "

Mr. Smith's attorney sought a lesser term, citing abuse to his client in childhood, including beatings with an extension cord, belt or a branch, which the lawyer said were so severe the young Smith once sought police protection.

Mr. Smith began drinking at the age of 8, started using marijuana and cocaine at 13, and eventually dropped out of school, according to his attorney.

Because many of his family members were also substance abusers or had been in prison, Mr. Smith "hardly had a chance from the beginning to become a responsible, law-abiding citizen," defense lawyer Paul Garrity said.

Mr. Smith was 17 when he was first arrested on drug charges, Assistant U.S. Attorney Natasha Tidwell said, and he had re-offended repeatedly, justifying his being sentenced as a career criminal.

Mr. Balba is currently being held on $100,000 bond.

Mr. Smith, who is serving his sentence in a federal penitentiary in California, will be returned to Massachusetts to face the murder charge in "the next few weeks," Mr. Warke said.

"But time is on our side in that he's held in a secure facility and won't be leaving any time soon," he said.; 203-731-3342