Lawrence MA, A Lawrence police officer was arrested Monday on suspicion of child rape following a monthlong investigation, according to the Essex District Attorney’s Office.

State police detectives assigned to the Essex DA’s office arrested 49-year-old Carlos Vieira in Haverhill without incident.

Vieira, of Lawrence, has been charged with two counts of aggravated rape of a child and two counts of indecent assault and battery on a child younger than 14.

The Essex District Attorney’s Office launched the investigation in January when the victim’s mother reported that her son, who was 13 years old at the time, had allegedly met the defendant using a social media app and engaged in sexual activity with him last summer.

“I am angry, sickened, dismayed, saddened by the allegations and charges,” Lawrence Mayor Dan Rivera said in a statement. “We have worked very hard to improve and uplift the professionalism of the Lawrence Police Department.

“We have fired and forced out many officers who did not meet and could not stand up to the code of conduct and the high level of professionalism that my office, the chief of police and the men and women and leadership of the Police Unions have worked to establish.

“If (the allegations are) found to be true, we will move swiftly to remove the officer involved. This is a travesty.”

Vieira is expected to be arraigned Tuesday in Lawrence District Court. He has been placed on administrative leave by the Lawrence Police Department.

Lawrence police Chief Roy Vasque said Vieira has been a member of the department since November 1999.

“This is an ongoing investigation, but the allegations against Officer Vieira are extremely troubling, and we take them very seriously,” Vasque said.