KANSAS CITY, MO. — Seventeen Kansas City police officers who formerly worked in a unit that failed to properly investigate crimes against children have been disciplined, with seven of the officers no longer working in the department, Police Chief Rick Smith announced Tuesday.

Smith’s announcement came after a nearly three-year internal investigation into the department’s former Crimes Against Children unit . The investigation began in 2015 when police officials learned detectives weren’t correctly investigating rapes, child molestations and other crimes against children, in cases generally between 2011 and 2016.

The discipline ranged from letters of reprimand to termination.

The conclusion of the investigation “marks the end of a regrettable time period” where Kansas City, Missouri, police failed to serve these victims, Smith said.

“I want to apologize to the children and families who did not receive the service they should expect from us,” Smith said.

Smith attributed the unit’s failures largely to its organizational structure and also “personal failures among commanders, supervisors and detectives,” such as failing to address large individual caseloads, The Kansas City Star reported .

Investigators identified 149 cases that had been “severely mishandled,” in some cases showing “gross negligence” by detectives and possible efforts to cover up failures. Detectives sometimes left evidence in drawers for months, even years, sometimes without any note to indicate what case the evidence accompanied, the investigators found.

“Most, if not all” of the families involved in those cases have been notified of their case’s status, Smith said.

The division now has a new staff of 10 detectives and two sergeants and further staffing remains a top priority, Smith said.

James Anderst, a child abuse pediatrician and director of the child abuse and neglect division at Children’s Mercy Hospital, said in an interview before the findings were announced that before the internal investigation, detectives seldom showed up for forensic interviews where specialists recorded child victims describing crimes against them. He said advocates were frustrated but had no way to force a law enforcement agency to do anything.

“Everyone kind of knew it was a black hole but there wasn’t a lot that we could do about it,” he said.

Platte County Prosecutor Eric Zahnd said the new staff of the Crimes Against Children Unit has shown marked improvement in responsiveness and investigations.