Police said the boy's paternal grandparents, Richard E. and Ruth A. Landers, abducted him in July 1994 because they were "upset over pending court proceedings" regarding his placement.
Police spokesman Sgt. Ron Galaviz said it appears the boy's father was never in the picture. Lisa and Richard Harter had married a year earlier.
Authorities believe the grandparents took the boy from their home in Wolcottville and fled. They were charged at the time with misdemeanor interference with custody, which was bumped up to a felony in 1999. But the charge was dismissed in 2008 after the case went cold.
Investigators reopened the case in September when Richard Harter turned over the boy's Social Security card to an Indiana State Police detective.
That turned up a man with the same Social Security number and date of birth living in Long Prairie, Minn., about 100 miles northwest of Minneapolis. A driver's license photo for the man appeared to resemble Landers, police said.
Indiana State Police then contacted Minnesota law enforcement agencies, which began investigating along with the FBI and the Social Security Administration.
The grandparents were found living in nearby Browerville, Minn.
"By all accounts, it didn't appear he suffered from any abuse, either physical or mental," Galaviz said.