Mandelbaum pleaded guilty in May.
Authorities say he sexually assaulted a 12-year-old boy last August.
The boy's father had briefly left him unattended in a restroom at the Monmouth Service Area in Wall as he cared for another sibling.
The father returned to find Mandelbaum molesting his son.
At the time of the arrest, Mandelbaum was already under community supervision for life for two prior sex offenses.
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Information from: Asbury Park Press, http://www.app.com
