Decades after the unidentified bodies of a woman and a 10-year-old boy were found in separate states beside a Southern interstate highway, investigators now say they were a mother and son and the boy's father has confessed to killing them.

The case was cracked thanks to an online DNA database, help from international police and a consultant whose work led to an arrest in the Golden State Killer investigation, authorities in North Carolina and South Carolina said Tuesday.

But investigators in both states said they had never stopped trying to solve the 1998 cases that they never knew were related, separated by 215 miles apart along Interstate 85.

"I always kept the case file box under my desk, where it was purposefully in my way. Every time I turned, I hit it with my leg. I did this so the little boy couldn't be forgotten," said Orange County, North Carolina, Sheriff's Maj. Tim Horne, who worked the case from the beginning.

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More than 20 years after the bodies of Robert Whitt, left, and Myoung Hwa Cho were found 215 miles apart in separate states beside Interstate 85, investigators now say they were a mother and son and the boy's father has confessed to killing them. AP

North Carolina authorities even enlisted experts to create a sketch and a bust reconstructing the appearance of the child. But despite wide-spread dissemination, no one was able to identify him.

Investigators had no idea the cases were linked until December 2018, when consultant Dr. Barbara Rae-Venter reviewed the latest DNA tests on the boy's body, Orange County Sheriff Charles Blackwood said in a statement. Rae-Venter's work with online DNA databases had earlier helped lead to an arrest of a man in California charged with 26 counts of murder and kidnapping in California in the 1970s and 1980s.

The boy's remains were found in September 1998 by workers mowing grass on a frontage road near I-85 in Durham, North Carolina, Blackwood said. DNA testing showed he had Asian and Caucasian parents.

Rae-Venter matched the child's DNA to DNA from a close relative who had submitted the information to an online database. After contacting the relative, investigators learned the boy was Robert "Bobby" Adam Whitt, who was born in Michigan and raised in Ohio, Blackwood said. He also said they were given strong evidence his mother — who had disappeared the same year as her son — was also dead.

Meanwhile, deputies in South Carolina had found an unidentified woman whose nude body was dumped in the woods beside I-85 in May 1998, Spartanburg County Sheriff's Lt. Kevin Bobo said. Her hands had been bound and she had been suffocated.

After DNA testing confirmed the victims were mother and son, investigators in the U.S. enlisted the help of Korean authorities and international police to identify the woman as Myoung Hwa Cho.

Cho's husband, the boy's father, is serving time in federal prison on unrelated charges. After being questioned several times he confessed to killing his wife and son, Bobo said.

Authorities aren't releasing his name because he hasn't been charged in the killings yet. Charges may not be filed until investigators figure out exactly where the two victims were killed, Bobo said. Investigators think the woman and her son were killed somewhere else and dumped beside the interstate.