It had already been reported that Trump's name had made the 329-candidate nomination list, though it now appears to have done so by questionable means.
It's the second year in a row that someone has nominated Trump for the prestigious prize after assuming the identity of a qualified nominator, said Olav Njolstad, secretary of the Norwegian Nobel Committee.
Concerning "the nomination of the United States president, I can say that we have good reason to believe it is a fake nomination", Olav Njolstad, non-voting secretary of the Nobel Committee, had told Norwegian public broadcaster NRK earlier this week.
The Norwegian Nobel Committee will announce this year's victor in October.
Rune Skjold, from Oslo police force's economic crimes unit, on Thursday confirmed reports the Federal Bureau of Investigation was contacted for assistance.
Skjold said the earlier letter was subjected to a thorough and lengthy forensic examination, which the new letter is also likely to undergo. Among those entitled to propose names are members of parliament and government, former laureates and some university professors. CNN said that the nomination praised Trump's "vigorous peace through strength ideology, used as a threat weapon of deterrence against radical Islam, ISIS, nuclear Iran and communist China".
The Prez reportedly got the nom from an anonymous American for his "ideology of peace by force" - which sounds like an oxymoron - but Nobel peeps were suspicious. The committee keeps the names of nominators secret for 50 years, unless they agree to make themselves known.
Njolstad said Thursday that it was the first time a fake nomination has been submitted "by stealing another person's identity". The five members of the Nobel committee that selects the victor are also allowed to submit names during their first meeting of the year, which was held on Monday.
2017's Peace Prize went to nuclear disarmament group ICAN for its decade-long campaign to rid the world of the atomic bomb.