The father and aunt of murdered toddler Cyrus Belt have sued the child's accused killer, Matthew Higa, as well as the boy's mother and the state Department of Human Services.

The suit was filed in state court late yesterday by attorneys for David and Lisa Belt, the father and aunt of the 23-month-old child who was thrown to his death from a freeway overpass two years ago this Sunday.

Higa, the alleged killer, is awaiting trial on a charge of murder. His lawyer in that case, Randall Oyama, could not be reached for comment on the lawsuit.

The suit alleges that Higa, 24, "obtained custody" of the victim "and caused him to sustain fatal injuries by throwing him off a freeway overpass."

Higa lived with his father in the same Punchbowl apartment building where Cyrus Belt lived with his mother, Nancy Chanco.

The suit alleged that Chanco was a "neglectful custodial parent" and charged that she was a drug user "who tested positive for crystal methamphetamine as recently as January 11, 2008, six days before the (fatal) incident."

Chanco couldn't be reach- ed for comment on the suit.

Chanco was not present at her apartment when her son was allegedly taken by Higa.

She has said that she left the boy with her father, Lilo Asiata. Asiata told police he let a neighbor take the child for a walk, according to court documents and DHS records.

The new lawsuit alleged that Chanco "repeatedly left Cyrus Belt with others who did not provide proper care" for the child and that her negligence "was a substantial factor in causing Cyrus Belt's injuries and death."

The state Department of Human Services and its Child Welfare Services Branch "knew or should have known of defendant Chanco's dangerous drug use and neglect of Cyrus Belt" and failed in their "legal duty and responsibility to timely remove Cyrus Belt" from Chanco's custody, the suit charged.

Toni Schwartz, spokeswoman for DHS, said the department had not yet received a copy of the suit and could not comment.

According to DHS records previously released by department director Lillian Koller, Cyrus' death came after at least six separate child welfare investigations into Chanco's handling of Cyrus and his two siblings.

Three of the cases resulted in findings that Chanco neglected her children.

In June 2006, Chanco was accused of abandoning Cyrus to allegedly use drugs, according to DHS records.

But none of the cases resulted in termination of Chanco's parental rights.

Under state guidelines, drug abuse by the parents is usually not sufficient cause to remove a child from the parents' care. To remove a child, the parents must be found to have severely abused and neglected the child.

Hawai'i law defines abuse and neglect to mean physical injuries such as substantial bruising, bleeding, malnutrition, broken bones, sexual molestation, failure to provide medical care and other physical dangers.

The lawsuit seeks unspecified monetary damages from the defendants.

David Belt, the father of Cyrus, was serving a state prison sentence for drug offenses when his child died.

He was released from prison last year, according to court records.