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It was used to slaughter first graders at Sandy Hook, murder Batman fans at Colorado movie theater, kill county workers at a holiday party in San Bernardino.

Now a descendant of the AR-15 semi-automatic rifle — a Sig Sauer MCX — has the dubious distinction of being the weapon of choice for a homosexual-hating gunman named Omar Mateen who is being blamed for the worst single-day mass shooting in U.S. history.

The lethal weapon was found early Sunday amid the 50 casualties of the carnage at the Pulse nightclub in Orlando, Florida.

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CNBC: The Rise of the AR-15

In the aftermath, President Obama once again railed at the ease with which domestic terrorists bent on killing as many people as possible can get their hands on high-powered guns and rifles.

Mateen bought his gun legally just last week in Florida, the feds said Sunday.

And the latest killings only added to the bloody pedigree of the AR-15 and its emulators.

Here are some of the other mass shootings in which the lethal rifle figured:

Dec. 2, 2015 — The AR-15 was one of the weapons Syed Rizwan Farook and his wife Tashfeen Malik used to kill 14 people and wound 22 more in an attack on the Inland Regional Center in San Bernardino, California.

Oct. 1, 2015 — Christopher Harper Mercer fatally shot and assistant professor and eight students in a classroom at Umpqua Community College in Roseburg, Oregon. He was armed with an AR-15 and other weapons.

June 7, 2013 —John Zawahri was armed with an AR-15 when he went on a rampage at the Santa Monica Community College outside of Los Angeles. He killed five people and wounded four before he was killed in a shootout with cops.

Dec. 14, 2012 — Adam Lanza used an AR-15 purchased by his mother to murder 20 first graders and six staffers at the Sandy Hook Elementary School in Newtown, Connecticut. He used a handgun to kill himself as the cops were closing in.

July 20, 2012 — The AR-15 was part of James Holmes’ arsenal when he opened fire during the midnight screening of "The Dark Knight Rises" at a movie theater in Aurora, Colorado.