The suspect in a deadly River North attack fatally shot a 24-year-old man because he thought the man had punched his father’s friend during a brawl early Saturday outside a popular bar, prosecutors said Monday.Jeffery Campos, 20, was ordered detained by a judge during a Monday hearing in which Campos faced first-degree murder charges.Campos, of Cicero, was arrested 12 minutes after the shooting that erupted about 3:40 a.m. after Campos and three of his friends left Mother Hubbard’s Sport Bar in the first block of West Hubbard Street and began fighting with the the 24-year-old victim on the sidewalk outside the bar, prosecutors said.The still-unidentified victim stepped in and threw two punches at a man in a yellow shirt to try and stop the fight and get him off of his friends, prosecutors said.The victim, who was not armed, then left the fight and backed away from it, but began watching it unfold as Campos, who was standing in the street wearing a black hoodie, watched the victim. and covered his face with a black mask, prosecutors said.Campos covered his face with a black mask, then stepped forward, extended his right hand, and fired one shot, hitting the victim in his head.The victim “immediately collapsed to the ground,” prosecutors said.A muzzle flash was visible on the police observation device video that captured the attack. The still-unidentified 24-year-old was taken to Northwestern Memorial Hospital, where he was pronounced dead, police said.As Campos and a witness, who grabbed two backpacks, began running east on Hubbard then south on State, an off-duty Chicago police officer working security heard the shot and saw them darting down the street, prosecutors said. The officer spotted what appeared to be a handgun in Campos’ waistband and saw them both remove their shirts, prosecutors said. They were arrested in an alley which turned into a dead end. A gun that was “still hot to the touch,” was found under a black T-shirt that was among several items found with Campos and the witness, prosecutors said.They were arrested, and after Campos was advised of his rights, he told police he shot the victim because he thought the victim had punched his father’s friend, who was wearing a yellow shirt, prosecutors said.According to prosecutors, Campos is on first-time weapon offender probation for an aggravated unlawful use of a weapon charge, for which he was sentenced to 18 months in March.Campos is due back in court Oct. 23.