The Federal Bureau of Investigation released a study Wednesday that revealed an increase in number of deaths over the last decade where a gunman wounds or kills multiple victims, commonly occurring in crowded places.

The FBI analyzed 160 'active shooter incidents' defined in the study as "individuals actively engaged in killing or attempting to kill people in populated areas (excluding shootings related to gang or drug violence)."

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From 2000 to 2013, they found out that 486 people had been killed in mass shooting incidents in the country while about 557 more were injured, bringing the total to more than 1,000 casualties over the 13-year span.

In 40 percent of the cases, the gunman committed suicide after killing several people while 60 percent entailed incidents where the shooting had already ended before authorities arrived.

Meanwhile, the study also revealed that 70 percent of the shootings occurred in either a business establishment or an educational institution.

Most of the mass murderers have been found out to be male, with only six incidents having female shooters.

Mandated by a law signed by U.S. President Barack Obama requiring the Justice department to investigate mass shootings in 2013, the study was prompted by catastrophic mass shootings over the past two years.

In one incident in 2012, 20 children and six adults at Sandy Hook Elementary School in Newtown, Connecticut were killed after a gunman opened fire in the school.

Another mass shooting occurred at a movie theater in Aurora, Colorado in the same year where dozens were also killed.

Just last year, 13 people were killed in a mass shooting incident at the Washington Navy Yard where the shooter was killed during a shootout.

An advocate for stricter gun control, Obama's other weapon regulating proposals have been blocked by legislators allied with giants in the guns and ammo industry.

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