Davis’ strength lay in community policing and prevention in crime hot spots, said Northeastern University criminologist Jack Levin. “The new commissioner has to do the same thing.”

Former Boston cop Tom Nolan said he expects “movement” behind internal minority contenders: “If you want to change the promotions system, that’s a pretty tall order. You’re going to have to get in line and fight different unions. Is this an attractive job for a national candidate? Maybe not.”