The longtime TV director, 51, has pleaded guilty to charges of child pornography, the Associated Press reports.
Mr. Alexander was charged with promoting a sexual performance by a child and possessing an obscene performance by a child.
Digital files of the alleged material were found in Alexander’s New York home.
Alexander will be sentenced in early May. He could face up to 7 years in prison.
The TV veteran has directed top shows like The Blacklist, The Tomorrow People, Raising Hope, Lipstick Jungle, Royal Pains, Rescue Me, Burn Notice and Lizzie McGuire, as well as 32 episodes of Law & Order.