Researchers who study active shooter incidents say the Brown University shooting is highly unusual, based on decades of data examining similar attacks across the United States. 

Dr. Kyle Gamache and Dr. Matt Zaitchik, psychology professors at Roger Williams University, have published two studies analyzing nearly 150 active shooter events nationwide. 

In their research, they say they found no other case in which the shooter remained unidentified and at large for an extended period of time. 

"I can think of no event that we looked at that the individual escaped and escaped unknown," said Gamache. 

The suspect in the Dec. 13 shooting at Brown University that killed two students and wounded nine others, was found dead in a storage facility in Salem, New Hampshire Thursday night.

"Having this line of research, this was so atypical," said Zaitchik. 

According to their research, the majority of active shooter events, about 74% end with the shooter taking their own lives or being apprehended or killed by police on the spot:

• Shooter committed suicide: 41% 
• Shooter killed or subdued by police: 33% 
• Shooter voluntarily ends rampage: 13%
  
• Victim or Bystander stopped the attack 7%  

"These events usually are very compressed in time, very violent, and end quickly," Zaitchik said.

Appearance of exit strategy

They added that the prolonged nature of this case is not the only anomaly. Based on what is known so far in the investigation, researchers say the suspect appeared to have an exit strategy, something they say is unlike any other active shooter event they have examined. 

Zaitchik, a Brown alumnus, noted the shooting occurred inside Barus & Holley, a building on the fringe of campus with less surveillance. 

The apparent planning and stealth with which the person of interest allegedly entered and exited the building stands out in the research, the professors said. 

"It's baffling to me," Zaitchik said. "I wish law enforcement well in trying to track down all this information." 

The researchers also said the uncertainty surrounding the case has stirred fear within the community, drawing comparisons to the prolonged anxiety felt in Boston during the manhunt following the Marathon bombing.