Vicious dogs that attack and maim people and other dogs are being put back on the streets because of lax oversight by the agency that's supposed to protect the public, the NBC4 I-Team has found.

Poor enforcement of city laws and policies by the Los Angeles Department of Animal Services leaves the city’s residents and surrounding communities vulnerable to attacks by dangerous dogs.

"It was like alligators biting you, because their jaws were so strong," said Dmytri Shyrokov, who was brutally mauled by two off-leash dogs while jogging in Studio City. Shyrokov required dozens of stitches, lost part of a testicle, and may not be able to father children. The city has lost track of at least one of the dogs who attacked him.

Dogs with a history of violent behavior are being returned to their owners or are unaccounted for -- raising the possibility they could attack again, the NBC4 I-Team found.

"I thought the system was going to protect me, but nothing happened," says Diana Chingos, whose Jack Russell terrier was killed when a loose pit bull attacked it in a Hollywood parking lot.

"The pit bull locked its jaws around my dog's midsection, and it literally crushed my dog's internal organs," Chingos told NBC4, about that off-leash pit bull who killed her beloved dog "Kelsey."

After the attack, Chingos asked for a city hearing to have the pit bull, named Hemi, declared as "dangerous." By law, Animal Services can declare a dog that viciously injures or kills as "dangerous," which means it has to be confiscated and humanely euthanized so it won't attack again.

"These dangerous dogs, these dogs that kill other dogs, should be taken out of circulation," Chingos told NBC4.

Animal Services can also order the owners of a violent dog to remove the animal from the LA city limits to a new owner.

But the Department of Animal Services said "evidence did not exist" that Hemi was dangerous, and simply returned the pit bull to its owner, Mario Osorio, even though he had a history of complaints that he let his pit bulls run off-leash, which is illegal.

The Department ordered Osorio to keep Hemi on a leash and wearing a muzzle, whenever he took the dog out of the house. But the I-Team caught Osorio violating that order day after day, letting Hemi and another pit bull run off-leash through his neighborhood.

When the I-Team asked the General Manager of the Department of Animal Services, Brenda Barnette, if she was concerned that an off-leash Hemi could kill or hurt again. Barnette replied, "Correct."

Dmytri Shyrokov is also worried that one of the dogs that mauled him could also attack someone else.

"They were ripping me apart. They just wanted me dead," is how Shyrokov described Romeo and Emelia, two pit bulls that were off-leash and lunged at him while he was jogging on a path in Studio City in September 2013.

Romeo locked his teeth onto Shyrokov's arms, while Emelia latched onto his groin--tearing one of his testicles, according to a report with Animal Services.

Shyrokov was rushed to Cedars-Sinai hospital, where he had stitches to repair dozens of bites, but doctors couldn't save part of the testicle which Emelia had bitten.

Again, Shyrokov asked Animal Services to declare Romeo and Emelia "dangerous" so they couldn't attack again.

Animal Services did declare Romeo "dangerous" because he had a history of attacking, but said there wasn't enough evidence to declare Emelia "dangerous."

The city simply ordered Emelia's owners to "permanently remove your dog" outside the LA city limits to new owners, and to provide Animal Services the name and address of the new owners.

But the I-Team discovered the city lost track of Emelia and doesn't know where the pit bull is currently. NBC4 tracked Emelia to a Santa Clarita subdivision, where neighbors don't know of her violent past.

Animal Services general manager Brenda Barnette admitted to the I-Team the city might have made a mistake by not declaring Emelia a "dangerous" dog " so she couldn't attack again.

"Is it possible there was human error made (in this case)? Yes there is. But I can't rewrite history at this point," Barnette said.

The I-Team also found instances where dogs that attacked people should've been impounded, but weren't.

To be sure, it is not just pit bulls that attack and kill other dogs and people.

"Any dog could have the potential of attacking and every owner needs to be aware of the potential of their own individual dogs," says Michael Chill, owner of Animal Services Dog Training and Behavior in Los Angeles.

When asked - on camera - if Animal Services could do a better job of protecting public safety from vicious dogs, Barnette said "I always believe we can do better."