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EDMOND, Okla. -- Edmond Police are investigating a sexual assault and the victim is the suspect's grandmother.

The woman's own 15-year-old grandson was arrested for the crime.

Police are not talking about the case but the reports say plenty.

Sunday police arrested 15-year-old Trevon Isaac after his 59-year-old grandmother called 911 and said Isaac had raped her in her sleep.

Court documents state the boy's grandmother said when she woke up Thursday morning "her privates were hurting and she noticed her panties were missing."

She later found them "under her bed and they had been cut."

The woman told police she "takes medications at night for medical reason and the medications put her to sleep."

The next night she told police she slept on the couch and the woke up to "Isaac thrusting against her" and that he ran into the bathroom yelling "I just touched you."

The woman later called 911 and her son.

Her son picked up Isaac and also called police.

The victim's son said Isaac told him, "I cut her panties off while she was in bed" and "I had sex with grandma."

Court records state he also said that he "had sex with grandma on the couch."

The teen was arrested and booked into the Oklahoma County Jail on first-degree rape charges.

The victim was taken to the hospital.

Test results indicate she had been sexually assaulted.

Isaac's bond was set at $25,000.