TULSA, Oklahoma - A probable cause affidavit filed on Wednesday in Tulsa County District Court says a Skiatook teen told police he stabbed his great grandmother last month after being asked to do the dishes, then killed his little sister, who was the only witness.

Michael Devin Stanley, 19, has been charged with murdering 74-year-old Esther Driskell and 16-year-old Larisa Fraley. Their murders took place just miles apart but in separate counties.

Both siblings lived with Driskell in Skiatook in Tulsa County, and police say they were notified when a visitor came over on January 27 and found the senior citizen's body in a pool of blood in her hallway and her van missing, the affidavit says.

A witness also reportedly said they saw Stanley and Fraley yelling in the front yard, appearing to be frantic about the time of Driskell's murder. Stanley was holding a light-colored purse, the witness told police.

After his arrest, Stanley allegedly confessed to the homicides during questioning at the Osage County jail.

According to the affidavit, Stanley told police his grandmother "had been on him about ‘things' and had been asking for him to do the dishes."

He then admitted to stabbing her with a paring knife he retrieved from a kitchen drawer, the affidavit says.

The Oklahoma State Medical Examiner's Office reports it observed what appeared to be seven stab wounds to Driskell's chest, left torso and left arm, documents say. Police said the left side of her shirt was torn.

Stanley reportedly said his sister was in the home at the time of the stabbing. He took his grandmother's purse because her van keys were inside and the two siblings left in the vehicle, he said, according to the affidavit.

"He stated that he did not forcibly place Fraley in the van but that she did go with him," the affidavit says. "Stanley admitted that his sister Fraley wanted to call the police and he stated that he could not keep her with him forever like he wanted to."

Stanley told police the two drove around before pulling off on to Lake Road, near Tall Chief Cove in Osage County, where he stabbed his sister to death inside the van before walking away, according to the affidavit.

Later that evening, witnesses came forward to say they picked up a young man who was walking alone near Tall Chief Cove and offered him a ride to a Tulsa QuikTrip. They picked Stanley out of a photo lineup, police said.

When investigators went to the area where the witnesses said they picked up Stanley, they found the abandoned van and Fraley, who was dead from apparent stab wounds, documents say.

Stanley is being held without bond for first-degree murder.

Family told News On 6 that Stanley and Fraley went to live with their great grandmother because their own mother has been in and out of prison since 2006. Records show the woman currently is serving a 10-year sentence after police say she was driving under the influence in a hit-and-run crash in north Tulsa. According to the criminal initial filing in 2012, the victim of the crash had to have his leg amputated.