MANHATTAN - The NYPD Counterterrorism Bureau has issued an active shooter attack study to prep security if they are ever faced with a mass shooting.

In a breakdown of the study, the city's police department gathered data from different shooter attack cases, using it to take a look at the commonalities among the shooters. A graph in the study shows that most shooters had a professional or academic relationship with at least one of the victims. Less than one-third of the shooters had no relationship at all.

In 87 attacks that involved professional relationships, fewer than one-third were perpetrated by individuals who were no longer employed by the organizations at the time of the attack.

The entire study is more than 200 pages long and includes more than 300 shooter attack cases.