PORTLAND — Maine’s highest court has rejected the appeal of a South Portland man who is serving 45 years in prison in the drug-related killing of a Boston man whose body was found off the Maine Turnpike.

In a unanimous decision today, the Maine Supreme Judicial Court rejected Huy “Tony” Van Nguyen’s appeal seeking to overturn his 2007 murder conviction.

Nguyen was convicted in the fatal shooting of Dun Quoc Hgo, whose body was found in 2005 off the turnpike in York. Prosecutors said the shooting was a “premeditated execution” in retaliation for a drug rip-off.

Nguyen claimed the judge erred in his jury instructions, in allowing certain evidence at trial and in not declaring a mistrial based on statements made by a prosecutor during closing arguments.