Alejandro Mayorkas has criticised social media rhetoric following the killing of UnitedHealthcare CEO Brian Thompson as "extraordinarily alarming."

Speaking to CBS' Face the Nation, the Department of Homeland Security Secretary shared his shock at the "heroism that is being attributed to an alleged murderer of a father of two children on the streets in New York City."

Luigi Mangione, the man suspected of killing Mr Thompson, has pleaded not guilty to state terror and murder charges in a Manhattan courtroom.

Mangione entered his plea during a Monday morning (23 December) arraignment hearing. He faces 11 counts in New York, including first-degree murder in furtherance of terrorism, second-degree murder in furtherance of terrorism and multiple weapons offenses. The 26-year-old faces up to life in prison without parole if convicted.