RIVERSIDE, Calif. -- A man wanted in connection with the murder of a Fallbrook woman was found dead about 9 a.m. Friday in Riverside County, according to officials with the Riverside county sheriff's department.

Sheriff's officials said Jeff Nolen, 38, was found dead behind the wheel of his green 2000 Mercury Mountaineer sport utility vehicle, California license No. 5TOX730.

In a news release, the Riverside County Sheriff's Department said deputies responded to the call of an unresponsive male adult in a vehicle in the 500 block of Myrtlewood Drive near Calimesa Blvd.

Deputies arrived to find a deceased male in the driver's seat, according to the news release. The cause of death was undetermined and an autopsy was ordered.

The discovery Thursday of a 74-year-old homicide victim in her North County apartment led to the arrest of her adult granddaughter and prompted a manhunt for Nolen, the suspect's boyfriend, a San Diego County sheriff's official reported.

Deputies responding to a request for a welfare check on the victim found her dead at her residence in the 400 block of Potter Street in Fallbrook about 12:30 a.m., Lt. Dennis Brugos said.

Several hours later, detectives arrested 32-year-old Amy Jo Mitchell of Fallbrook at her Shady Glen Drive home in connection with her grandmother's death, according to Brugos.

The lieutenant declined to discuss evidence that allegedly implicated Mitchell in the slaying.

Nolen, a tow-truck driver, was Mitchell's live-in boyfriend and the father of her three children, Brugos said.