St. Petersburg, Fla. -- A Tampa man is facing manslaughter charges after investigators say he wanted to see if a flak jacket would repel bullets. Police say he shot his cousin in the chest killing him. A witness told detectives that 23-year-old Joaquin Mendez found the flak jacket and wondered if it still worked. That's when 24-year-old Alexandro Garibaldi said, "Let's see" and pulled out a handgun and shot the vest, killing his cousin. Investigators say there is a hole in the vest.

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A flak jacket is not a bullet proof vest -- though modern ones are often called that because they're made to sustain certain types of gunfire. The first ones in World War II were nylon vests with steel plates sewn in. Manufacturers have made them lighter over time. They can resist shrapnel but do not protect against gunfire from rifles or handguns unlike a ballistic vest which is made to absorb their impact.

10News WTSP wanted to find out how well ballistic vests work at protecting you and law enforcement from gunfire. Police warn you should never try to test out a flak jacket or a ballistic vest.

Officer Robert Lord of the St. Petersburg Police Department says,"None of these vests are truly bulletproof they're all bullet resistant."

Officer Lord is in charge of researching, ordering and fitting some 560 sworn officers in ballistic vests which he says is still an important layer of protection. He adds, "It's just a matter of reducing the officers risk of death or serious injury."

Lord says the vests can be hot under the Florida sun, and heavy when you factor in all the other gear they carry and even at a price tag of about $800 a piece they don't last forever. He says, "So this is an expiring product. It varies by manufacturer but it's very common in the industry to see a 5-year warranty. St. Petersburg Police is generous enough to play it safe and we replace them at 4 years for officers."

After 12 years on the force, Officer Lord says he's seen them get lighter and stronger. You can now wear them under your clothes or over your clothing in a special vest making it easier to slip on and off. Officer Lord says, "It's not perfect, but it's better to have some protection than none."

St. Petersburg Police also told us that different vests can be reinforced with special plates which make them able to resist a higher caliber of bullets.