Election Commission (EC) chairman Itthiporn Boonpracong said he welcomed the participation of the Department of Special Investigation (DSI) in a probe into alleged collusion in last year's Senate election.
Commenting on the probe's progress into the vote-rigging allegations, Mr Itthiporn said the EC has received 577 petitions over alleged misconduct since last year's Senate election.
So far, nine completed cases have been forwarded to the Supreme Court for further legal prosecution, he said.
Of the 577 complaints received, 220 cases were vote-rigging allegations, a violation under Section 77(1) of the organic law on the composition of the Senate, he said.
Among these 220 cases, 115 have been fully investigated, Mr Itthiporn said.
On Tuesday, the EC received three more alleged Senate vote-rigging cases transferred from the DSI.
He said DSI officials had been invited to work on these three additional cases with the EC.
The DSI transferred these cases after a preliminary probe found violations of the organic law on the composition of the Senate, which falls in the EC's jurisdiction.
The EC has been criticised for stalling the investigations of the Senate election and a lack of transparency.
Meanwhile, about 30 former Senatorial candidates, also on a reserve list, submitted a petition to suspend EC secretary-general Sawaeng Boonmee for negligence of duty after he reportedly failed to prevent collusion during the Senate election process.
The Senate election last year was complicated as candidates voted among themselves and the eligible professional groups on the district, provincial, and national levels.
The group said there was a probable reason to believe the EC may have tried to cover up the alleged acts, as no investigations were carried out.
In their petition, the group also asked that other agencies, such as the Royal Thai Police, DSI, the Anti-Money Laundering Office, and the Office of the Attorney General, participate in the investigation into Senate election collusion to create public trust and ensure the investigation is as complete as possible.
