A 35-year-old man, who shot himself near Harvard University a week ago, has left behind a 1905-page suicide note, an online document he had been working on for the last five years.

Mitchell Heisman shot himself at Harvard Yard on September 18.

His family and about 400 friends received the 1,905-page suicide note in a posthumous e-mail.

In the note Heisman wrote that he took his life as part of a philosophical exploration he called "an experiment in nihilism."

The lengthy document included 1,433 footnotes, a 20-page bibliography, over 1,700 references to God and 200 references to the German philosopher Friedrich Nietzsche.

Heisman wrote, "Every word, every thought and every emotion come back to one core problem: life is meaningless. The experiment in nihilism is to seek out and expose every illusion and every myth, wherever it may lead, no matter what, even if it kills us."

"If life is truly meaningless and there is no rational basis for choosing among fundamental alternatives, then all choices are equal and there is no fundamental ground for choosing life over death," he wrote.

He quoted former US President Thomas Jefferson and Albert Einstein in the lengthy document.

The New Jersey native, who had studied psychology in college, had told his family and friends he was working on "a history of the Norman conquest of England."

The chapters in the document are titled 'Philosophy, Cosmology, Singularity, New Jersey' and 'How to Breed a God.'

Heisman's friends said he bought the gun, a .38-caliber pistol, three years ago. They described him as being "cordial, considerate and quiet."

Heisman, a Jew, committed suicide in Harvard yard in front of a group of tourists, on the day of Yom Kippur, considered one of the holiest days in Jewish faith.