DENVER -- A third child, in less than eight months, has died after the Denver Department of Human Services investigated abuse allegations but failed to remove her from her parents.

Isidoro Valdez-Ruelas, 24, was charged Monday with first-degree murder and child abuse resulting in death in the death of 4-month-old Luz Valdez, according to court documents.

Call 7 Investigator John Ferrugia learned that about a month before Luz's Dec. 30 death, DDHS workers investigated complaints that Valdez-Ruelas was dropping the baby on the floor and on a bed when arguing with the girl's mother. The girl was not injured in those instances despite crying for several minutes afterward, a source said.

The human services worker determined Dec. 18 that the case had a high risk level and a high abuse score, but then on Dec. 26 -- four days before Luz's death -- Dept. of Human Services officials inexplicably determined that there were no safety concerns in the home.

In a statement to 7NEWS, the Denver Department of Human Services declined to comment and said, "By law we are not allowed to discuss the details of any case."

The case follows two other high-profile deaths last year of families who had extensive contacts with the Department of Human Services but were not taken from their family members or guardians.

Chandler Grafner, 7, died in May and his guardians are facing murder charges for allegedly starving the boy. Social service agencies from three counties had contact with the family, but DDHS did not follow up on an April complaint that the boy had not been to school.

The following month, Chandler was dead.

Neveah Gallegos, 3, died in September and her mother, Miriam Gallegos, and Miriam's boyfriend, Angel Ray Montoya, were arrested but then released without charges in the case, court documents show.

Denver police are continuing to investigate the case, said Lynn Kimbrough, spokeswoman for the Denver District Attorney’s office.

Human Services investigated allegations in July 2006 that Montoya, a registered sex offender, had sexually assaulted the girl, court records show. Prosecutors declined to file sex assault charges because they said they didn't have enough evidence to convict.

Denver Human Services opened a case on Neveah's family for six months after the sexual assault allegation. DDHS employees closed that case in January 2007, determining there were no child protection issues at this time.

Neveah's body was found Sept. 24 near West 10th Avenue and Perry Street in Denver, three days after her mother reported her missing, documents show.

After 7NEWS broke stories of DDHS actions in the cases, investigations were started into whether flawed procedures at DDHS led to the child deaths. There were also state investigations into the Grafner and Gallegos cases.

State investigators found some flaws in the way Denver and Jefferson County Human Services handled Chandler's case but did not fault Denver workers for deciding not to follow up on his school's complaint.

The investigations into Neveah's death and DDHS procedures are still ongoing.

In the most recent incident, a search warrant affidavit shows that Luz's mother told police she left the baby with Valdez-Ruelas on Dec. 28 at 2:10 p.m. at their apartment in 100 block of South Pennsylvania Street in Denver, and he called her saying Luz was very sick. She was taken to the doctor that day.

Medical authorities at Children's Hospital told police that Luz had bleeding on the brain and the injuries were consistent with abuse, according to the search warrant. She died Dec. 30.

Valdez-Ruelas is being held in the Denver County Jail without bond and is scheduled in court Wednesday. Through jail officials, he declined to be interviewed.

Luz's family buried the girl Monday.