(CBS) — Imagine this: A kidnapper takes an Oak Lawn couple’s newborn son in 1964.

Two years later, a boy matching his description is found and returned to the couple.

Now, it turns out, the boy they raised isn’t really their son. KLAS-TV in Las Vegas first reported the story; CBS 2’s Dana Kozlov picks it up from there.

“I also want to find out who I am and why I was abandoned,” Paul Fronczak says, reading from a letter.

It’s an emotional message he wrote to his parents — Chester and Dora Fronczak of Oak Lawn — after finding out they weren’t his biological parents after all.

The Fronczak saga began in April 1964 at the now-demolished Michael Reese Hospital. That’s where Dora gave birth to her son, Paul. Sixteen hours later, while she was feeding her son, a woman appearing to be a nurse told her the baby was needed for tests.

Dora handed her newborn over. Hours later, she learned her baby had been kidnapped.

A massive FBI hunt ensued. It went nowhere until two years later, when someone found a toddler –- the man who today goes by the name Paul Fronczak — abandoned outside a New Jersey store.

Absolute proof lacking, the couple adopted and raised Paul. But he had doubts, and recently, years after finding newspaper clippings of the kidnapping, he took a DNA test.

The person divulging the results said “there’s no remote possibility that you are the Fronczak baby,” Paul Fronczak said. “I was like, wow.”

He says Chester and Dora will always be his parents, but he’s haunted by questions.

“Is the real Fronczak baby still alive? Is it out there?” Paul Fronczak asks.

Chester Fronczak and his wife say they went through this ordeal almost fifty years ago and have no interest in talking about it now.

An FBI spokesperson says the case is uncharted waters, but it’s possible the bureau could reopen the case.