The quest to end the barbarism that has long dominated New York’s Rikers Island jail complex entered a new phase this week when the Justice Department announced that it planned to join a pending class-action lawsuit that charges the Department of Correction with failing to discipline officers engaged in abuse.

Preet Bharara, the United States attorney in Manhattan, said the city had not made enough progress in reforms to end the jail’s “deep-seated culture of violence,” which was documented in a lacerating report his office issued in August on the treatment of adolescent inmates.

That report provided bloodcurdling examples of sadistic violence against young people and called for an extensive overhaul of departmental operations. It recommended, for example, that adolescents be removed from Rikers Island and placed in a facility elsewhere. It insisted that the city improve officer training and disciplinary measures and that incidents of assaults be reported accurately and promptly.

The August report warned the city that it would find itself in court if the recommendations were not carried out quickly. Any confidence in the city’s commitment was shaken in September when The Times reported that city officials had withheld from prosecutors crucial portions of a report on violence at Rikers Island and that correction officials involved in reporting data that was inaccurate had been promoted. Prosecutors pointed to those promotions in court documents filed this week as an example of the city’s “failure to put in place qualified managers and supervisors who are committed to and capable of reducing the level of violence.”