1. Mayo’s arrest was legal. Based on the issue at hand; there was a dead man on the ground, a loaded weapon, a broken bottle, and alcoholic beverages around the location. First thing the officer did was arrest Mayo, not for his safety but for the officer’s safety. All of the evidence at the scene paints a potential incident or crime was committed.
2. Law enforcement did not need a search warrant. They were responding to a call from the bar or location in the area were shots were fired. If the police where there on a basic suspicion or needed to do a search for any specific reason, then a search warrant would be required, but in this case the cops responded to a crime scene and saw all of the weapons in plain view.
3. The police are able to pick up the broken bottles and gun without a search warrant. It would not be the same police that detained Mayo, it would be a backup force if possible that secured the crime scene. Least case, if the police did not have any backup support, they would recover the broken bottle and weapon from the crime scene and take it back to the law enforcement agency for evidence processing.