Prison sentence Luigi Mangione is facing as he is charged with murder as 'an act of terrorism'

Manhattan District Attorney has defended the move to charge Luigi Mangione with murder as an act of terrorism as the story continues to develop.

On December 4, Brian Johnson was shot and killed in what is believed to have been a targeted attack by 26-year-old Luigi Mangione.

Johnson was shot twice in the back and in the leg as he left the Hilton hotel in Midtown Manhattan, where UnitedHealthcare - the medical insurance company he ran - was holding an investors' meeting.

Mangione was arrested following a nation-wide search and was apprehended after he was recognized in a McDonald's in Pennsylvania.

New York prosecutor Alvin Bragg spoke to reporters on Tuesday (December 17) and said Mangione hoped to 'sow terror' in his actions.

Luigi Mangione was arrested after being recognized in a McDonalds (Jeff Swensen/Getty Images)

He said this after a grand jury indicted Mangione with the additional murder charge on Tuesday, after they had already charged him with murder in the December 4 for the killing of Johnson.

If he is convicted on all counts, Mangione could face a mandatory sentence of life in prison without the possibility of parole.

Speaking to reporters, Bragg said: “This was a frightening, well-planned, targeted murder that was intended to cause shock and attention and intimidation.

“It occurred in one of the most bustling parts of our city, threatened the safety of local residents and tourists alike, commuters and businesspeople just starting out on their day.

“The intent was to sow terror.”

Mangione's defense lawyer in New York, Karen Friedman Agnifilo, has not yet commented on this move by the grand jury.

Under New York law, a terrorism charge can be brought when an alleged crime is 'intended to intimidate or coerce a civilian population, influence the policies of a unit of government by intimidation or coercion and affect the conduct of a unit of government by murder, assassination or kidnapping'.

A fundraiser has been set up to help pay for Luigi's legal fees (Pennsylvania Department of Corrections via Getty Images)

Since Mangione has been arrested, some people on social media have taken to defending the alleged killer’s actions, something the police have since commented on.

New York Police Commissioner Jessica Tisch said any attempt to rationalize Mangione's alleged actions was 'vile'.

Tish has said: “There is no heroism in what Mangione did.

"We don't celebrate murders and we don't lionize the killing of anyone."

Despite this condemnation, many people across the world have donated to a fund that is set on paying towards Mangione’s legal defense.

Set up on Christian site GiveSendGo, over $147,000 have been raised so far.

Defending the campaign, GiveSendGo’s communications director Alex Shipley said: "We believe every person is entitled to due process in a court of law — not in the court of public opinion.

“To be absolutely clear, we do not support or condone vigilante justice. However, people have a constitutional right to a strong legal defense, and access to that defense should not be reserved only for the wealthy or those who fit a particular narrative."