The state’s highest court today affirmed a former Cambridge resident’s two first-degree murder convictions for the 2006 slayings of Julio Ceus and Natalie Sumner during a robbery in Allston, Suffolk County District Attorney Daniel F. Conley said.

The decision means CRAIG SMITH (D.O.B. 2/10/69) will continue to serve the back-to-back life terms imposed following his 2007 trial, Conley said. Smith is serving additional concurrent terms ranging from five to 30 years for trying to murder one of Ceus’ roommates, pointing a gun at another, and robbing the victims of their cash and cellular phones.

Ceus, 33, and the roommate lived at the Kelton Street murder scene. Sumner, an 18-year-old resident of Franklin, New Hampshire, was romantically involved with Ceus’ brother and was staying at the scene while the brother was at work on the night of Jan. 8, 2006.

Smith claimed on appeal that the trial judge should have allowed one of his peremptory challenges and not seated one of the 16 jurors initially empanelled, and that the judge also should have allowed testimony suggesting an unknown third-party culprit may have been responsible. In a unanimous, eight-page decision authored by Justice Robert Cordy, the Supreme Judicial Court rejected both claims.

The trial judge found during jury selection that Smith’s attorney was using his peremptory challenges to eliminate some prospective jurors from the panel because of their ethnicity. The judge denied one of those challenges and the juror was seated; she was ultimately selected as an alternate, however, and did not take part in deliberations.

“[W]here a juror that a judge has seated over the defendant’s challenge does not participate in deliberations, the defendant does not face the risk of the juror he perceives as biased against him influencing the verdict in his case,” Cordy wrote.

Smith’s trial attorney also sought to pin the murders on an unknown, third-party culprit through testimony about a problem Ceus had with a woman and one of her friends, as well as a sleepless night in which he worried about “stuff in his past.” After a hearing, the judge determined that there were “no substantial connecting links between this mystery person and this crime” and that the evidence of a third-party culprit was “speculative.”

“The defendant cannot escape the consequence of the vague nature of the proffered testimony,” Cordy wrote. “[T]he evidence is of minimal probative value, and its admission would pose a danger of unfair prejudice to the Commonwealth … The judge properly weighed these considerations, and correctly deemed the proffered evidence inadmissible.”

During eight days of trial, Suffolk prosecutors proved that Smith and Ceus knew each other well and that Smith called Ceus on his cell phone just minutes before the murders, prompting Ceus to open his apartment door.

Smith and a still-unidentified second gunman entered and ordered everyone present into the rear of the apartment. Four were forced to the floor at gunpoint; an elderly woman was forced to sit in a chair.

In the moments that followed, Smith demanded the victims’ cell phones and money. When they gave the assailants cash and the phones, Smith demanded more.

“That’s not all there is,” he said. “You’re lying.”

Smith then gave a signal and both assailants opened fire, unleashing a total of nine rounds that killed Ceus and Sumner and wounded Ceus’ roommate. Two additional female victims were physically unharmed.

In the days and weeks that followed, Boston Police homicide detectives developed damning evidence against Smith, including eyewitness identifications of him as the gunman, surveillance footage from a nearby camera that captured his car driving away from the scene just after the shootings, and cell tower records showing his phone followed a path from Cambridge, where he lived, to Brighton, near the murder scene on the night of the murders.

Assistant District Attorney Anna Kalluri of the DA’s Appeals Division briefed the case and defended the convictions before the SJC. Assistant District attorney John Pappas, formerly of the DA’s Homicide Unit and now his chief trial counsel, prosecuted the case at trial. Smith was represented on appeal by Stephen Maidman.