A 15-year-old Michigan boy admitted having sex with a 3-year-old girl, so enraging his father that the man pulled a gun, marched the teen to an empty lot and shot him through the head, the father's defense attorney said Tuesday.

The lawyer for Jamar Pinkney Sr., 37, said he will pursue an insanity defense as a judge in the Detroit enclave of Highland Park ruled that Pinkney should stand trial on first-degree murder, assault and firearms charges in his son's Nov. 16 death.

Defense attorney Corbett O'Meara said Pinkney's son's confession would have driven anyone crazy.

"There is no rational response to the rape of a child," O'Meara said after the hearing. "He was immediately remorseful and didn't seek to hide. He turned himself in to the police."

Authorities haven't said if they believe the teen raped the girl and police have said the matter is not part of their investigation. Wayne County prosecutor's office spokeswoman Maria Miller declined to comment Tuesday on the nature of the sexual contact.

Pinkney's confrontation with his son came a day after the 3-year-old underwent an examination at Children's Hospital of Michigan. Results of the exam haven't been released, but the teen's mother said they indicated her son "had molested" the girl. The Associated Press is not naming the girl or detailing her relationship to the teen to avoid identifying a victim of sexual assault.

Lazette Cherry testified Tuesday that her son told her about his contact with the girl in a conversation that stretched long into the night. She said her son called his father about 3 a.m.

"Daddy, can you please forgive me in your heart, forgive what I did?" she quoted Jamar Pinkney Jr. as asking his father.

The mother said the elder Pinkney agreed to come to the house later to talk further. Cherry's sister, Yolanda Cherry, testified that Jamar Pinkney Sr. arrived about 10 a.m.

Yolanda Cherry said she and her sister talked about getting help for the teen, while Pinkney Sr. said he spoke with the 3-year-old's mother and she wanted to press charges.

"Jamar, is there something you want to tell me?" Yolanda Cherry quoted Pinkney Sr. as asking his son.

"He got on his knees in front of his dad and said, `I'm sorry,"' the aunt said.

"What did you do?" she quoted the father as asking.

"I humped (the girl)," the teen replied. "I need counseling."

Pinkney Sr. didn't immediately respond, Yolanda Cherry said, and she left to visit her mother's upstairs apartment. She later heard screaming and banging and rushed down to find Pinkney Sr. holding a handgun and beating his son.

Both sisters testified Pinkney Sr. ordered his son to undress and marched him outside. The teen's mother said Pinkney Sr. ordered the boy to kneel in the grass, ignoring his pleas for mercy.

"I said, `Jamar, stop. Don't do this. Think about what you're doing,"' Lazette Cherry testified.

She said Pinkney Sr. stood behind the boy and shot him in the head, then walked around still grasping the gun.

"He didn't want anybody to go back and help him," the mother said. After Pinkney Sr. left, she rushed to her son's side.

"He's bleeding, blood coming out of his mouth," she said. "Somebody said, `Get some covers, cover him up, keep him warm.' So that's what we did."