In the end, the documentary was nearly left unfinished because a mysterious animal-borne illness felled the director during six months of post-production.
Harrison said the film was almost "too personal" to watch. He had been "on the dark side," raising both a python and a tiger in the 1980s. He lost two close friends who were strangled to death by snakes and eventually took on the crusade to keep people from even acquiring these animals in the first place.
There are 15,000 exotic cats in captivity in American homes, as well as 7.3 million reptiles.
Harrison noted that an estimated 3,400 tigers are living with ordinary families in Texas -- more than double the 1,400 that live in the wild in India.
In the film, Dr. Roger Pocholka, an emergency room physician at Miami Valley Hospital, laments, "I travel to Africa, and I see more fatal injuries in this country. You don't keep lions and cobras in the house. They are afraid and we should be too.
"I get angry at the animal specials that show how tame and manageable they are," he said. "We see them as cuddly, but they'll eat your face -- literally!"
The film's story follows the journey of Harrison and lion-owner Brumfield, who meet after Lambert's escape and capture. As the film opens, Brumfield is forced to confine Lambert and his mate Lacey in a small prison-like trailer.
Knowing things could get worse, Brumfield says, "I have to shoot him."
But he so desperately loves Lambert, who nuzzles against his master, that he adds, "I have two shells and a gun, then I'll kill myself."
Harrison confronts Brumfield and tries to convince him to find a better home for his beloved lions -- which, by the end of the film, include two baby cubs -- at a zoo or game reserve.
"That animal trusted you when you bought him," he sternly tells the owners. "He loved you and he trusted you, and you went against his trust."
"Am I a hero or a villain?" asks Harrison, who has worked with exotic animals for 37 years. "If you've ever seen a small child constricted by a python or a person mauled by a big cat or a beautiful creature put down when there is no reason to be killed, it's horrible."
Webber began to follow Harrison on his rescue routes after reading the officer's book, "Wildlife Warrior."
"I always look for unique scripts and I wanted to take the audience to a world they had never seen before," said Webber. "I was fascinated and didn't quite believe these things could be true. I started doing my own research and realized it was the elephant in the living room. It was going on all over the country."
Webber, 40, who came from a narrative film background ("Like Dandelion Dust," 2009), built on Brumfield's desire to do the right by his lions.
"Terry was, to me, was such a fascinating character study," said Webber. "He was suffering from depression ... and I connected with him and knew the struggles he was having -- just to get out of bed in the morning and do something. He found a connection with these lions and they are what gave him the reason to go on. ... Those animals helped him."
Webber also gave thumbnails of news events happening real-time: A woman's hands and face are ripped apart by a chimpanzee in Stamford, Conn.; a Virginia Beach woman suffocates as her neck is crushed by a python; a 2-year old is strangled in his crib by a pet snake; and a California trainer is killed by his bear.