JACKSONVILLE, Fla. -

Two Rottweilers killed an 83-year-old man in Alabama. A two-day old infant was mauled to death in Pennsylvania. A two-year-old girl died after she was bitten by a pit bull in West Virginia.

Jim Crosby has worked all of these cases as a canine crime scene investigator.

The retired Jacksonville, Fla., sheriff's lieutenant relies on forensic tools such as bite molds and measurements, necropsy results and saline swabs. His goal: to determine why a dog mauled a person, and whether it should be rehabilitated or destroyed because of its behavior.

"I speak dog," said the 54-year-year-old Crosby, who lives with three curly coated retrievers and two miniature wirehaired Dachsunds. "No, it's not whispering. There's no whispering involved."

Crosby says dog bites are often far more complex than they appear, and they shouldn't be handled with a knee-jerk reaction of instantly killing the dog.

Among the few forensic experts on dog bites in the country, Crosby is writing a book called "Working the Worst: A Guide to Investigating Dog Related Fatalities." It's intended as a manual for detectives and animal officers.

Jim Crosby with dog "I found that nobody ever applied the kind of stuff we did in police work to dog attacks," said Crosby, who is also the breed rescue chairman of the Curly Coated Retriever Club of America.

There aren't many in his line of work. Two men in California provide forensic evaluations and expert testimony during cases, and both are animal behavior experts. Crosby differs because he comes from a traditional law enforcement background.

His second career began soon after he retired in 1999 after 22 years with the Jacksonville Sheriff's Office. First he became a trainer. Then he started thinking about dog behavior and realized there weren't any standardized law enforcement investigation procedures for dog bites.

Now he travels the country to help animal control departments, lawyers and police agencies with dog-mauling investigations. He's worked on 17 fatal dog bite cases in recent years, paying his own way for some of those first consulting jobs. Now, he's getting paid by animal shelters, prosecutors and even defense attorneys to investigate. But he'd like to find a university, insurance company or other business that will pay him to do research and forensic work.

Through his work, Crosby met Victoria Stillwell, a dog trainer and host of cable channel Animal Planet's "It's Me or the Dog," and a friendship blossomed. The two are scheduled to give presentations at the National Dog Bite Awareness Conference in Denver on Nov. 2.

"I'm more like his nurse, where I hand him the stuff, the saline and the swabs," Stillwell said recently on her weekly podcast. "Where he and I really work well together is that we watch the dog's behavior. We really find out why. What was in the dog's circumstance that made this dog do this?"

The cases Crosby investigates are often grim. In many, the offending dogs haven't been properly socialized or trained, and the victims are often children. So far in 2012, there have been 27 fatal dog bite cases reported nationwide; and thousands more non-lethal bites.

"It's usually a perfect storm of things," he said. "Most commonly, there's some kind of human failure."

He is currently working the case of an 83-year-old man in Leeds, Ala., who was killed by his neighbor's two Rottweilers.

Crosby is helping police and prosecutors build a manslaughter case against the dogs' owner, who was found to have 33 other Rottweilers on his property. Crosby has looked at photos of the attack, interviewed witnesses and analyzed necropsy results of the two responsible dogs, which were shot by officers after the attack.

In 2005, Crosby helped authorities prosecute a West Virginia man whose pit bull killed a 2-year-old girl. It was the first time a person in that state had been convicted of involuntary manslaughter as a result of a dog attack. Crosby found the dog had been improperly cared for, poorly trained and not adequately socialized. He said the owner also encouraged aggressive behavior that led the dog to bite five adults before the fatal attack.

"These are specialized kinds of homicides," he said. "But the weapon is a semi-sentient being operating both under a person's direction and somewhat on its own."

Sometimes, Crosby's evaluations don't involve a death. In September, he evaluated a pit bull named Memphis in Bloomfield, N.J. The dog was picked up off the streets by the local animal shelter. A resident who is a dog trainer spent several days training Memphis in his home and wanted to adopt him - but the shelter didn't feel the dog was ready for adoption and Crosby agreed.

Crosby, who was paid by the township to evaluate the dog, feels Memphis can be adopted with some additional training, but is "not ready for a run at an average Joe Blow home," either.