Authorities say they are investigating the discovery of unidentified remains of three children, believed to be between 3 and 7 years of age, in Memphis, that could have been there for years.

At a news conference on Wednesday, Memphis Police Chief Cerelyn "CJ" Davis said a skull was found near a wooded area by someone walking their dog on March 8, who reported it to police. Because of limited lighting conditions, police said a more extensive search was scheduled for the next day. That led to further searches over the days and weeks. On March 10, a K-9 cadaver dog led authorities to a drainage pipe later searched by camera; however, no remains were found during that search, according to officials. 

On April 1, investigators found another skull, this one in the drainage system, Davis said.

The following day, search teams in the area found another 14 bones, Davis said.

About 170 personnel from various agencies, from the FBI to search and rescue personnel, were scouring the area on Wednesday, seeking more evidence that could help identify the deceased, Davis said. Police said they hoped to close the portion of the investigation at that specific search area crime scene on Wednesday evening.

The cause of death is still undetermined and investigators are working to identify the individuals.

Authorities believe there is no active threat to the public. Davis said the children were not people reported as missing in the Memphis area.

"Someone knows of missing children that we have discovered in this area," Davis said. "This is heartbreaking, it's disturbing and at this time we have numerous resources to help us to identify these young people and bring closure to this investigation."