JEFFERSON CITY, Mo. - One day before the scheduled execution of a Missouri man convicted of killing a state trooper two decades ago, Gov. Mike Kehoe announced his decision to deny clemency.

Lance Shockley, 48, will be executed Tuesday at 6 p.m. for the murder of Missouri State Highway Patrol Trooper Sgt. Carl Dewayne Graham.

Graham was found shot to death outside his home near Van Buren in southern Missouri on March 20, 2005.

The governor's office said that Shockley shot and killed Graham due to the trooper's investigation into him. Officials were looking into his involvement in a crash where Jeffrey Bayless, a passenger in Shockley's car, was killed. Troopers believed Shockley to be under the influence of alcohol at the time.

Shockley was found guilty of first-degree murder and three aggravating factors in March 2009, according to the Associated Press.

The Missouri Supreme Court set Shockley's execution date in June after being on death row since May 2009. There had been attempts to appeal or request a new trial, but each was denied.

“Mr. Shockley has received every legal protection afforded to him under the Missouri and United States Constitutions, and his conviction and sentence will remain for his brutal and deliberate crime. The State of Missouri has—and will continue to—pursue justice to the fullest extent of the law. Carrying out Lance Shockley's sentence is evidence of our commitment to the pursuit of justice,” Kehoe said in a release Monday.

Shockley will be put to death at the Eastern Reception, Diagnostic and Correctional Center in Bonne Terre, Missouri. 

The organization Missourians to Abolish the Death Penalty released a statement shortly after the announcement was made, which reads, in part:

"Governor Kehoe's refusal to grant Lance Shockley clemency or appoint a Board of Inquiry is unconscionable. There is a reason that governors can grant pardons, clemency, and boards of inquiry. Courts make mistakes. Governors can fix those mistakes. As a new governor, some hoped he would prioritize a higher authority than political ambition. Once again a governor has let us down."