"He said that a government person came around to talk to him later, but he told him to shut up and go away."
The book has been written using portions of a rough transcript of a video tape of the interview.
Mr Forgus said: "What I seen of him looked just like the one we see on television, with big eyes.
What I saw of him looked just like the one we see on television, with big eyes.
"There was a big round thing in the canyon. It was about 100 feet across.
"They put that on a truck and hauled it away. They wouldn’t let us get very close to it either."
The testimony has met with doubters already.
In a blog post on website theufochronicles.com Roswell UFO expert Kevin Randle said: "Though Forgus didn’t know which branch of the service they were in, the US Army on their fatigues should have been a big clue.
He was asked if there were lights on the craft and he said, 'No, they went out when it banged into the wall in the creek'
"Though I’m not sure how he would have known that the lights went out when it hit because he wasn’t there."
He said the crash site location described by Mr Forgus matched that given by the late Frank Kaufmann, whose account "has already been discredited."
Mr Randle wrote: "He said he could see the bodies, though he didn’t have a good description of them.
Roswell UFO incident in pictures.
"He talked about the big eyes. He said 'Their eyes looked like the ones we see on television and the pictures of them.'
"But he was so far away, according to him, it is difficult to believe that he would have seen the eyes.
"The real clue is about having seen alien creatures on television.
"He just picked the most popular version of the aliens to describe."
Mr Randle claimed the roads surrounding the crash site would have been blocked so they would have been unable to even get there.
He added: "The other part of the story that fails is that they heard about this on the police radio, which seems unlikely, but even if that had been true, they wouldn’t have heard instructions on how to find the place.
"You can’t see it from the main roads, and the gravel and dirt roads into the area are quite rough and quite confusing.
"If you don’t know where you are going, you’d get lost. Without someone leading them in, or precise directions which wouldn’t have been broadcast, they would never have found their way to the crash site."
Asked what the author and Mr Mantle thought of the testimony, Mr Mantle said: "We remain open minded on the testimony documented bu Deputy Sheriff Forgus.
"We hope that by releasing this information now that others may be able to shed more light on it one way or the other."