Clint Van Zandt, a former FBI profiler and NBC News criminal analyst, said in the early days of an investigation like this, police try to rule out motives like drugs or robbery and hunt for anything the victims could have in common. They will comb through older crimes to see if any of them fit the pattern, and they will broaden the search beyond Tampa, he said.
"Normally when something like this happens, a serial offender would start out in neighborhood or community he's comfortable in a place he knows the way in and out and that territory may expand as he becomes more emboldened," he said.
Enzo Yaksic, who tracks data on serial homicides at Northeastern University, said the indiscriminate nature of the shootings could point to gang initiation rituals, but could also be the handiwork of a modern serial killer.
"The recent crop of serial murderers with anger-based motives strive to exact revenge on society with quick bursts of violence often within a tight geographic area aimed at those readily available to them," he said.