US Air Marshal in 'Quarantine' After Syringe Attack in Nigeria

Victim flown home on United flight to Houston.

U.S. law enforcement officials told ABC News they were alarmed by the bizarre, unprovoked attack because the assailant was apparently able to inject an unknown substance into the back of one of the air marshal’s arms.

The air marshal was traveling with a team of other marshals when the attack took place in an unsecured area of the airport terminal in Lagos, the officials said.

An FBI spokesperson said, “The victim did not exhibit any signs of illness during the flight and was transported to a hospital upon landing for further testing. None of the testing conducted has indicated a danger to other passengers."

Health experts say most infectious agents would not immediately manifest or make the patient contagious.

While the unknown assailant ran away and could not be located, officials said the other air marshals on the team were able to secure the needle and bring it on the flight for testing in the U.S.

U.S. air marshals travel undercover in plain clothes and it would not be immediately obvious to an attacker that his target was an American law enforcement agent, officials say.

“While there is no immediate intelligence to confirm this was a targeted attack, this is our reminder that international cowards will attempt to take sneaky lethal shots at our honorable men and women abroad,” said Jon Adler, the national president of the Federal Law Enforcement Officers Association.

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