D.C. Attorney General Karl A. Racine on Wednesday launched a review of police procedures after an officer was seen on video chasing and detaining a 9-year-old boy whose mother said had committed no crime.

Police announced separately that the officer involved in the incident is now under internal investigation. A department spokesman said that review includes trying to determine why the officer detained the child, who was not charged with a crime and was released from the scene into the custody of his mother.

The attorney general’s inquiry comes less than a month after another D.C. police officer detained a 10-year-old boy who was initially accused of committing an armed robbery. The youth was later exonerated after authorities reviewed surveillance video that captured the incident.

In a statement, Racine (D) called the latest incident “obviously concerning” and said his office, with acceptance from D.C. police and the mayor, would review how the department deals with children and compare those guidelines with those from other departments around the country.

Racine said his office, which prosecutes juvenile offenders in the District, will then “recommend what changes, if any, should be made to the manner in which police officers are trained on the proper way to interact with children.”

The detentions of the two children — on March 30 on Capitol Hill and on Monday evening in Columbia Heights — have sparked discussions among leaders and lawmakers in the District. In each case, video of officers handcuffing the children was captured by bystanders and broadcast on television news.

Under D.C. police guidelines, nearly everyone taken into custody is handcuffed to protect officers and the detainee from injury and prevent flight. Only juvenile truants and curfew violators are not handcuffed unless they become violent. The youth division and a high-ranking supervisor are also supposed to be notified.

Reaction to the detention of the 10-year-old in March was initially tempered in that police had accused him of threatening another youth with a pellet gun, and while Police Chief Peter Newsham said that video of the detention of someone so young was uncomfortable, it appeared to be within protocol. Criticism rose when the attorney general announced that the child had been wrongly accused.

Newsham said in an interview Wednesday that he viewed the most recent detention as an aberration among the more than 500,000 yearly encounters his officers have with the public, including the annual arrests of about 3,000 juveniles. He said that after the incident in March, the department began its own research into how other police agencies deal with children “to see if we can improve our practices.”

The chief said he was restricted in providing many details because the case involves a juvenile. But he said the review of Monday’s detention is to determine if it was “consistent with MPD policy.” He added that the incident is “not indicative” of the vast interactions his officers have with the public.

The detained boy’s mother said the fourth-grader was visiting relatives in Northwest Washington and playing when an officer confronted him about 7:30 p.m. Monday. The mother said that the boy had been leaning against a vehicle at 14th and Girard streets NW and that her son told her the officer ordered him to move away.

“My son said a slur to him and ran away from the officer,” said the mother, who spoke on the condition of anonymity and that her son’s name not be published.

A video from a bystander, first broadcast on WTTG (Fox 5) on Tuesday night, shows the child running, a denim jacket flapping in the wind, and the officer following and reaching for him. The boy falls, but it’s not clear if the officer grabbed him or the boy fell on his own.

The video shows the officer grabbing the boy’s jacket and then walking him to a police vehicle, holding both his hands. The boy can be seen squirming and crying as he is moved and as the officer starts to put handcuffs on him.

A relative came to the scene and called the boy’s mother, who drove to the location. The mother said officers could not explain to her why they detained her son.

“I asked them what crime had committed,” she said. “What harm was he doing to anyone? What threat was he? They couldn’t answer those questions.”

Luz Lazo contributed to this report.