It sounds like in custody but not arrested although "“He is believed to be our person of interest" so I suspect the arrest is a formality that is coming shortly. See how much you can get him to talk before formally charging him.Last I heard they had a 'person of interest' in custody but not arrested - caught in a McDonald's in Pennsylvania. That's been upgraded ?
Man in custody had a gun, mask and writings tying him to killing of UnitedHealthcare CEO: police
Police have arrested a 26-year-old man with a weapon consistent with the gun used to kill the head of the largest U.S. health insurer, New York’s police commissioner said Monday.
www.cp24.com
EDIT:
"He was being held in Pennsylvania on gun charges and eventually will be extradited to New York to face charges in connection with Thompson’s death"