Here are some items on the “shopping list,” of every extremist who has terrorized communities from Oklahoma City to Boston to Charleston, and now, Orlando:

Excitement. Camaraderie. Revenge. A need to belong. And, above all, notoriety.

Prof. John Horgan of Georgia State University knows the list well. He has interviewed terrorists from Ireland to Indonesia to Pakistan, and written books on the mindsets of terrorists. Omar Mateen, who slaughtered at least 49 people and wounded more than 50 in an Orlando nightclub last weekend, seemed to be checking some items off that list, Horgan said.

In terms of personality, extremists share much, from Timothy McVeigh, whose rage was aimed at that the federal government, to Dylann Roof, who loathed African Americans, to Mateen, whose anger was aimed at the LGBT community and apparently stoked by a twisted interpretation of Islam. All of them are narcissists, experts say. All of them want to be remembered as doing something “big.”

In the case of Mateen, authorities have said he claimed allegiance to the Islamic State or ISIS after he stormed the Pulse nightclub and had taken hostages.

“Or he used the Islamic State affiliation to elevate homophobic bigotry,” said Horgan of the GSU Global Studies Institute. “For reasons that are unclear to us, he decided that this is how he wants to be remembered.”

That walk down the path down radicalization often begins in plain sight of family members, co-workers and friends, experts say. But some loved ones and associates just don’t want to see what’s in front of them before it’s too late, said author and Brandeis University Prof. Jytte Klausen, founder of the Western Jihadism Project, which studies Islamic terror groups in the West.

She pointed to Mateen’s selfies and photographs, which, taken as an online album, show him trying on different identities. In one he poses in a t-shirt emblazoned with a New York Police Department logo on the front. In another he is shirtless with close-cropped hair. In yet another he mugs for the camera, dapper in shirt and tie. Then there’s the image of him in a skull cap typically worn by some Muslim men.

Couple physical changes with behavioral ones — either subtle or overt — and they can signal a potential problem, Klausen said.

“Changing behavior, picking fights, changing appearance, bragging about ties to an extremist group or ideology, if you can check more than one box, that’s when you should start being concerned,” Klausen said.

So, what is path to radicalization? Can someone actually self-radicalize by simply watching propaganda online?

“Where things get tricky is the radicalization process itself,” said Horgan.

Horgan, Klausen and others explain that process here on myajc.com.