A man killed during an attack on an escort may have been a serial killer, according to investigators.

Neal Falls, 45, arrived armed with a handgun at the Charleston, West Virginia home of a woman he had found on an escort website. In the boot of his car, meanwhile, were multiple sets of handcuffs, a machete, two axes, a bullet-proof vest, a shovel and a bottle of bleach.

When the woman, who wishes to be identified only as Heather, opened the door, she says he placed the gun to her stomach and asked her, "live or die?"

"When he strangled me, I grabbed my rake, and when he laid the gun down to get the rake out of my hands, I shot him," she said. "I grabbed the gun and shot behind me."

Heather then ran out of the house bloodied and shouting for help. Police found Falls dead inside the home, but the case took on another dimension when they searched his car and found the horrifying evidence of his intentions.

They immediately began to suspect that he had been planning not just an attack, but murder. And this may not have been the first time.

"It's likely that Mr Falls is a serial killer," said Steve Cooper, Charleston Police Department Chief of Detectives. "I believe she saved lives by shooting Mr Falls, based on what he did to her and based on the items found in his car."

The FBI is now searching Falls's past for clues that the former security guard from Oregon with no notable criminal record may have harmed other women.

Meanwhile police departments across America investigating cases which have gone cold are looking at Falls as a possible culprit.

About 100 miles west of Charleston, in the town of Chillicothe, Ohio, at least six woman have vanished in recent months. Investigators there are now investigating the possibility that Falls was responsible.

In Illinois and Nevada there have been recent cases of online escorts being murdered with implements similar to those found in Falls's car.

Heather will not be charged in Fall's death, with police treating the incident as self-defence.

She says as soon as she saw Falls, "I knew he was there to kill me".

“I fought men my whole life,” she told the Gazette-Mail newspaper. “I guess I had to be ready for that guy.”