Hjorth’s sentence was cut from 11 years and four months to 10 years, 11 months and 25 days.
The other man convicted of the killing, Finnegan Lee Elder, is serving a definitive term of 15 years and two months.
Elder was found guilty of killing Cerciello Rega with 11 stab wounds inflicted by a combat knife he had brought over from the US while Natale Hjorth assaulted the slain officer’s partner at the end of a chain of events sparked by a drug deal that went wrong.
Tuesday’s ruling was the third time Natale Hjorth’s case was addressed at the appeals-court level.
In March, the supreme Court of Cassation upheld the conviction but sent the case back to the appeals court to see whether the jail term should be reduced.
Last year, a court granted a request from Hjorth to be released from prison to serve his sentence under house arrest at his grandmother’s home in Fregene, a town on the coast near Rome.
Natale Hjorth and Elder were both given life prison terms in the trial of first instance, but those sentences were gradually knocked down during the appeals process.
ANSA