Two workers with the Mississippi Department of Child Protection Services are on administrative leave over the death of a 4-year-old girl and the severe injuring of her younger sister.

The department had months ago received two reports of alleged abuse involving the girls, but the resulting investigations found no evidence to substantiate the allegations. A supervisor and front-line investigator involved in the case were suspended Tuesday, news outlets reported.

Armani Hill, 4, and Lailah Hill, 3, were severely beaten last week while in the care of their mother’s boyfriend, James Christopher Anderson, police said.

Anderson then walked the children a quarter mile (0.4 kilometers) to his mother’s home in Natchez as one of the girls repeatedly fell from her injuries, investigators said. Armani was hospitalized and died. Her sister was in critical condition as of Wednesday.

Anderson is charged with child abuse. The children’s mother, Lakeisha Marie Jones, is charged with child deprivation. Investigators said she knew Anderson was abusing her children and failed to stop him. It is unclear whether Jones has an attorney who could comment on her behalf.

Coroner James Lee said Armani died from blunt force trauma.

“There’s indication that the abuse of these young babies had gone on for quite some time,” Armstrong said.

The Clarion Ledger reports the Mississippi Department of Child Protection Services was told in December that Armani and her sister were covered in cigarette burns.

Lea Anne Brandon, the department’s director of communications, said policy required an investigation launch within 24 hours, but a probe didn’t start until days later. Brandon acknowledged the deadline wasn’t met, saying investigators unsuccessfully attempted to contact the family. It’s unclear if other investigations have been delayed by similar issues.

The department received another complaint in January after Jones took Lailah to a clinic with a head wound. The young girl told doctors that Jones threw a walkie-talkie at her, but later said Armani threw the toy. Again, an investigation wasn’t launched until days later.

Investigators found no evidence supporting the abuse allegations.

The department later opened another investigation, allowing the children to stay in the home amid investigator visits. A social worker last visited in May and closed the case the day before Armani was killed.

Brandon told WLBT-TV that an investigation into worker actions is continuing.

“Where was the ball dropped? Where we should have done more … we have yet to reach a final conclusion,” she said.