Federal prosecutors in Mexico have asked a judge to issue arrest warrants for 22 employees of a day care center where a 2009 fire killed 49 babies and toddlers and injured 70 other children.

The prosecutors' office said Wednesday that the judge has until Aug. 18 to rule on the request. The warrants would be for the equivalent of involuntary homicide or manslaughter, and causing injuries.

While prosecutors say 29 people remain on trial in the case, nobody has been convicted.

Relatives have questioned the wisdom of charging low-level employees.

The fire in the northern city of Hermosillo exposed serious deficiencies in security systems at the day care center. The center caught fire after an air conditioning system overheated next door at a warehouse used by the Sonora state government.