The case of Trayvon Martin, a 17-year-old unarmed teen allegedly gunned down by a neighborhood watchman, prompted intense criticism of "stand your ground" laws that justify use of a deadly weapon.

These laws increase manslaughter and murder and don't deter violent crimes, according to a recent study by Cheng Cheng and Mark Hoekstra at Texas A&M University. They also might escalate violence in otherwise non-lethal situations, such as Martin's case.

According to the study:


Florida, Martin's home state, was the first to adopt such a law in 2005. Since then, 20 other states have followed.

The uproar over Martin's case led the U.S. Commission of Civil Rights to say they'd review the laws.

Here's a graph showing homicide rates among states that had "stand your ground" laws and those who didn't. The blue line represents states that have "stand your ground laws."

DON'T MISS: A minute-by-minute timeline of the Trayvon Martin case >