Missouri prosecutors are seeking the death penalty for a 35-year-old man accused in the killing of a couple from Arkansas who is already serving life sentences in six slayings in Illinois.

Prosecutors in Jefferson County south of St. Louis filed notice on June 8 of their intent to press for Nicholas Sheley's execution if he's convicted in the Festus, Missouri, killings of Jill and Tom Estes of Sherwood, Arkansas. Police say the couple was attacked outside a hotel after leaving a graduation party in 2008. Sheley is accused of loading their bodies into a pickup truck belonging to another of his victims and dumping the bodies near a gas station a short distance away.

Sheley is already serving six life sentences at Pontiac Correctional Center for a string of killings that began in his Illinois hometown of Sterling. Four victims whose bodies had been bludgeoned with a hammer were found in a Rock Falls apartment. They ranged in age from 2 years to 29. The other victims were a 65-year-old man whose body was found behind a Galesburg grocery store in northwestern Illinois and a 93-year-old man killed in Sterling.

In February, Sheley was extradited to Missouri where, unlike in Illinois, offenders can be sentenced to death.

Jefferson County Prosecuting Attorney Forrest Wegge declined comment Monday, as did the assistant prosecutor handling Sheley's case. The June 8 court filing outlining the state's decision cites Sheley's convictions in the six Illinois killings as well as three other aggravating circumstances, including his attempt to rob the Arkansas couple while committing an "outrageously or wantonly vile, horrible or inhuman" killing.

Neither of Sheley's two St. Louis-based public defenders could be reached for comment Monday morning. An arraignment is scheduled for July 6.