By Walt Hunter

PHILADELPHIA (CBS) – Ten years after her son Richard Petrone and his girlfriend Danielle Imbo vanished, along with their pick-up, after leaving a South Street restaurant, the pain for Richard’s mother, Marge, only grows worse.

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“I’d like to say it gets easier, but it doesn’t, it gets harder every day, knowing there’s someone still out there who did this,” she told CBS 3’s Walt Hunter.

“What happened to him? Where is my son?”

Now, hoping to catch the criminals who abducted and, the FBI believes, murdered the couple, there will be new billboards from Maine to Florida, a major national escalation of their investigation.

“For his sake, we won’t stop until we get answers,” stated Mrs. Petrone.

“I’m a little more confident that I had been in the past that we’ll get to a conclusion,” added FBI Special Agent Vito Roselli.

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Roselli, who has worked the case since the day the couple disappeared, says leads developed from an FBI push last February on the 10th Anniversary of the disappearance, sparked the new, national expansion of the probe.

“With those leads we are following through,” Agent Roselli explained.

“Hopefully to a good conclusion.”

Meanwhile, Marge Petrone was among the hundreds of thousands on the Parkway Sunday, praying for answers.

“There’s no way I’m not going to Mass to pray for my son, he’s going to help me, I know it,”she explained.

Her daughter and Richard’s grandson left their wishes on the Knotted Grotto, hoping their prayers and the new FBI initiative will at last bring justice.

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Anyone with information is asked to call 1-800-CALL-FBI.