How did Krakauer become familiar with Chris McCandless's story and then write Into the Wild?

Into the Wild, the book based on Christopher McCandless’
life was written by Jon Krakauer and published in 1996. In 1993 Jon had written an
article about Christopher for the Outsider magazine. The immense response that Krakauer
received for the article motivated him to delve deeper into the life of Chris and this
resulted in the book.

Krakauer made all attempts to ensure
the facts which form the basis of the book were accurate. These were collected by
meeting hundreds of people which included family members, friends, colleagues and many
others who had come across Chris while he was on his adventure that finally ended with
his death in Alaska. Krakauer personally visited the locations where Chris had been to
get familiar with the environment where he spent his
days.

An important aspect that helped Krakauer connect to
Chris’ life was his own ambition and several attempts made to spend time in the
wilderness detached from others. The marked similarity of their lives is reflected in
his words

I
got away with it. Chris didn't. That's the only
difference.