But in a nation with more mass shootings than all other rich countries combined, as a matter of sheer volume, there will be incidents in which an unknown shooter with an unknown motive makes an escape. It is just a matter of the odds and a little intelligent preparation on the part of the assailant. This appears to be the situation at Brown, and as much as that is unsettling, it is not evidence of police incompetence. In my own homicide cases when I was a chief of police, more often than not, an arrest required a multiday interstate hunt, one spanning the continent, and these were instances in which the perpetrator had been known to the victim or witnesses. When the investigative starting point is the complete chaos of a shooting scene, some arrests just take time, and some cases are just hard to solve.