FBI investigates voter fraud in key states

>>> the election is not for another 11 days but investigations are already under way into cases of alleged voter intimidation and fraud. nbc's national investigative correspondent michael isikoff has more on this. michael, good morning to you.

>> savannah, good morning. as election day grows closer, watchdog groups are worried about a surge in dirty tricks . apparently aimed at keeping voters from the polls, and the fbi is now on the case. the official looking letters are showing up across florida , challenging voters' citizenship and their right to vote. those getting them are outraged.

>> i was ballistic when i read it.

>> basically they were saying they were questioning my citizenship and were implying that they were going to eliminate from being able to vote.

>> reporter: fake letters, which threaten non-registered florida voters with arrest and imprisonment, were all post marked in seattle. up to 100 have been reported in 28 florida counties . the fbi is trying to track down the perpetrators. florida officials are alarmed.

>> this is an attempt to intimidate voters in one of the most important states in the united states in a national election.

>> reporter: members of both parties and independents have received the phony letters, although a majority seem to have gone to republicans, even one to the state gop chairman. watchdog groups say it's one of many dirty tricks popping up aimed at voter suppression .

>> we've seen earlier in the election cycle than previous years these nefarious underhanded tactics by shadowy groups to restrict the ability of responsible americans to vote.

>> reporter: these include billboards in minority neighborhoods in pennsylvania warning vote fraud is a felony. they are now coming down after a public outcry . in arizona some hispanic voters received official notice listing the election as november 8th , two days after election day . just this week, a conservative activist group cut the son of democratic congressman jim moran in an undercover video sting seeming to go along with a plan to cast fraudulent battlllots.

>> he said he was trying to humor the person who was asking him but did resign from the campaign. meanwhile another investigation of a republican operative accused of throwing voter registration forms in a dumpster. the operative, colin small, who couldn't be reached for comment, had previously worked for strategic allied consulting, a consulting firm fired by the republican national committee last month after employees turned in hundreds of suspicious registration forms in florida , including some with fake addresses, like a shell gas station . at the time the head of the firm, nathan sprewall, told nbc news he was the victim of a few bad apples that worked for him. in the case of the phony letters in florida , the state gop chairman that got one received it at his business address from which he writes campaign contributions . that's a sign, the source says, that the perpetrators may have been targeting voters they found on a public database of political donors. savannah?

>> michael isikoff in our washington newsroom, thank you.