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On Friday, the department said it received a complaint against the officer involving a young victim.
The Youth Services Unit and Internal Affairs Unit began an investigation and obtained arrest warrants later that day.
On Sunday, the officer was found dead in the median of Interstate 95 in Wilson County, the State Bureau of Investigation said Tuesday.
The SBI identified the officer as Wade Lane Lee Jr., 32.
The state agency said Lee's death "has been determined to have been caused by an apparent self-inflicted gunshot wound."