The case involving a 20-year-old man accused of impregnating an 11-year-old girl months after he admitted to the relationship's existence is under administrative investigation, police say.

Carlos Jacinto Cobo-Perez told Phoenix police detectives in December that he was in a relationship with the girl shortly after her mother discovered a hickey on her neck and suspected Cobo-Perez was involved, according to court documents.

Police interviewed Cobo-Perez over the phone on Dec. 10, 2018, when he acknowledged knowing the relationship was wrong and that he would end it.

Records don't say whether Cobo-Perez was arrested or charged after police interviewed him.

When asked if the Phoenix Police Department was investigating why Cobo-Perez wasn't arrested after he admitted to the relationship, the department confirmed there was an "administrative investigation" but refused to comment further.

Police booked Cobo-Perez into a Maricopa County Jail on two counts of sexual conduct and one count of aggravated assault. He is being held on a $150,000 bond and his next scheduled court hearing is May 28 in Maricopa County Superior Court.

Reach the reporter Perry Vandell at 602-444-2474 or perry.vandell@gannett.com. Follow him on Twitter @PerryVandell.

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