During interviews with police, Cody also confessed to having a complicated history with his sister that led up to her death, officials said.
KWTV reported Major Michael Arterbury with Del City Police Investigations said, "We have learned during our investigation that there was an intimate relationship between the two of them."
Arterbury added, "He did give detailed statements in his interviews and confessed to the crimes that occurred."
Police talked with family members, who said the relationship between Cody and Heather had been going on for years. Their family home is just a few blocks from the school where Heather was killed in the early morning hours of Aug. 13, officials said.
According to KWTV, Garde allegedly told police they were doing drugs together when they walked to the school.
Arterbury said, “We believe an assault occurred there and probably some sexual activity occurred there,” KWTV reported.
Cody claims the violence began consensually, saying Heather “told him to hit her, but he did not want to,” police said.
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Police said Garde allegedly told detectives he continued to beat her while they engaged in sexual activity before he carried her back to their home, authorities said. By morning, investigators said she had died.
Arterbury said Heather was taken to the hospital and was pronounced dead.
Cody was arrested and charged with second-degree murder and incest, officials said. He is being held without bond.
Mid Del Schools released a statement that explained that “the incident is not connected to our school or team."
Arterbury noted, "It did occur after hours. No school, no students, nothing involved there."
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