PARK TOWNSHIP, Mich. (WWJ/AP) – The state appeals court won’t upset the conviction of a western Michigan man who was charged with killing his sister and brother-in-law, 26 years after their deaths.

The star witness at trial was Ryan Wyngarden’s wife, who told Ottawa County jurors that he immediately admitted his role in the fatal shootings back in 1987. She even saw the bodies at the Park Township home but says she remained silent for decades because Wyngarden had threatened her.

READ MORE: Science of Weather: O'Shea Solar Park

Wyngarden was charged in 2013 and convicted of first-degree murder. He’s serving a no-parole sentence.

The appeals court said Wednesday it found no errors in Wyngarden’s trial that would justify a reversal of the verdicts. The victims were 22-year-old Gail Brinks and 28-year-old Rick Brinks.

READ MORE: Michigan Matters: Motor City's Italian Connection Grows!

Police have said Wyngarden was jealous of the newlyweds’ success and wanted to keep secret sexual encounters he and his sister when they were teens.

Wyngarden testified in his own defense during the trial, and was grilled on the stand about the alleged sex episodes with his sister at age 12 to 15 years old.

“I wouldn’t have killed my sister over this,” an emotional Wyngarden said, according to Mlive.

MORE NEWS: MSP, Metro Detroit Police Crack Down On 'Move Over' Law

TM and © Copyright 2015 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2015 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.