Former federal police chief Mick Keelty has begun his investigation into 1375 missing votes from the West Australian Senate ballot.
Mr Keelty was in Canberra on Tuesday ahead of travelling to Perth to gather evidence and interview witnesses.
The investigation is expected to take two weeks.
An AEC spokesman said all evidence would be given to Mr Keelty and his independent advice would be an "important input" into whether the commission petitions the Court of Disputed Returns in the next 40 days.
The court could decide on a fresh election of WA senators.
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A number of parties, including Labor, the Palmer United Party and Wikileaks, are also considering taking the matter to court.
The 1255 above-the-line ballots and 120 informal votes disappeared during a recount by the Australian Electoral Commission after the September 7 federal election.
The formal recount began at the central senate scrutiny centre in the Perth suburb of Northbridge on October 17.
The recount took a fresh look at informal ballot papers plus about 1.2 million ballot papers where voters marked the ballot paper above the line.
The votes counted including not only those cast at WA polling places but other voting centres around Australia, overseas and by post.
Up to 120 AEC staff were involved in the count, which used a computerised system called EasyCount Senate.
When it was discovered some ballots were missing, the AEC conducted what it described as a "very thorough" search before publicly admitting the error.
On Monday, the AEC declared the WA Senate result as three Liberal, one Labor, one Green and one Australian Sports Party.
The AEC plans to run a "model" of the missing votes to see if they would have changed the result.
The writ for the WA Senate election will be returned on Wednesday.
