They fear he could be Bin Laden's youngest son, 19-year-old Hamza, who has been dubbed the 'Crown Prince of Terror'.
Three of Bin Laden's wives and several of his children were taken into custody by Pakistani intelligence forces after the raid - but now it appears one of his sons may have evaded capture.
The revelation came as fascinating new details emerged of the U.S. assault force dispatched to find Osama Bin Laden, including the president's insistence that it had to be large enough to fight off hostile Pakistani soldiers if need be.
President Obama's determination to send a large task-force into Pakistan shows he was willing to risk a confrontation with the country, a close ally, if it meant capturing the Al Qaeda mastermind.
News of Hamza's apparent escape emerged during the interrogation of Bin Laden's three wives by Pakistani investigators.
Officials told ABC News the women had revealed one of the terror leader's sons had not been seen since the raid - but the source did not confirm which one.
Another son, 22-year-old Khalid, was confirmed dead by the U.S. military. He is believed to have been one of the men shown in graphic photos taken in the aftermath of the raid and released to Reuters last week. Read More