Carl Barbour, Jr., 18, was taken into custody last week on another robbery charge.
His mugshot was shown to the couple, and police say they identified him as one of the attackers.
Police are still looking for a second suspect.
Investigators say this appeared to be a well-planned attack.
A couple from Florida returned to their hotel room, but had trouble getting in. While they worked the lock to their room, two men rushed them, knocked them to the ground, and started beating them.
Police say it was a planned attack: The suspects jammed the door before the couple arrived.
The attack happened outside room 138. Police say it's likely the suspects watched the couple walk across the street to a shopping center, and waited for their return from a movie at 10:25 p.m.
Anyone with information is asked to call Delaware State Police at 1-800-TIP-3333.
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