Walter's Palmer's killing of Cecil the lion puts hunting in the cross hairs

It is, for some well-heeled foreign visitors, the ultimate African experience: the thrill of hunting a lion, one of the so-called "Big Five" animals whose habitats are under increasing pressure from human encroachment.

Walter Palmer, the hunter who injured the beast with a crossbow before it was shot dead 40 hours later, has become the hunted, the target of online vitriol and of US authorities.

Investigators for the US Fish and Wildlife Service have knocked on the front door of Palmer's house, stopped by his dental office, called his telephone numbers and filled his inbox with emails. Palmer couldn't be lured out of hiding.

"I'm sure he knows" the government is looking for him, said Ed Grace, chief of law enforcement for the US Fish and Wildlife Service. "We've made repeated attempts to try and get in contact with him."

Palmer, a dentist in Minnesota, has fallen off the radar since Tuesday, when reports first surfaced identifying him as the hunter of Cecil the lion. In one of his only public statements, Palmer said on Tuesday "I deeply regret" killing "a known, local favourite" and that he relied on local guides. He said he was led to believe the hunt was legal.