A former city detective who tried to cover up a gangland murder orchestrated by his cousin was properly sentenced to more than 12 years in prison, a federal appeals court said yesterday.

The 2nd U.S. Circuit Court of Appeals in Manhattan rejected a request for leniency for Michael Silvestri, who was sent to prison in 2003 by then-Judge Michael Mukasey, who last year became attorney general.

In May 2003, Silvestri was sentenced to 12 years and seven months in prison after a jury found him guilty of helping to conceal his cousin Joseph Brideson’s role in the January 1998 shooting of Joseph Conigliaro. In May 2006, Mr. Mukasey rejected a request to reconsider the sentencing. In an appeal, Silvestri’s lawyers argued Mr. Mukasey did not give an adequate reason.

The appeals court said Mr. Mukasey acted properly and explained his reasoning. At the time of his original decision, Mr. Mukasey said he considered the seriousness of Silvestri’s conduct and the difficulties Silvestri would face in prison as a former police officer.

The appeals court said Mr. Mukasey’s reasons were more than sufficient to justify the sentence. Silvestri’s prison term was at the bottom of the range recommended under federal sentencing guidelines, but judges have the option of dropping below the recommended range.

A message for comment left with a lawyer for Silvestri was not immediately returned yesterday.

Conigliaro, an alleged loanshark, was shot in a car in Brooklyn. Apparently unaware that Brideson was connected to the attack, he managed to drive to a social club and pick up Brideson, who drove him to a hospital where he died, authorities said.

At trial, the government said Silvestri removed bullet casings from Conigliaro’s car, though he was acquitted of destruction of evidence.

A detective had also testified that Silvestri asked him to fake a police report about interviewing a possible witness in the case.

Brideson, convicted of conspiracy to murder Conigliaro, is serving a life sentence.