The Department of Special Investigation's (DSI) money-laundering probe into alleged collusion in last year's Senate election will likely wrap up in three months, Justice Minister Pol Col Tawee Sodsong said on Wednesday.
About 140 senators could also be summoned for questioning by at least 41 DSI investigators and prosecutors from the Office of the Attorney-General (OAG), he said.
Charges will be pressed if enough evidence is found, Pol Col Tawee said.
The minister denied the DSI investigation was a witch-hunt for political gain.
Meanwhile, a group of 81 senators petitioned the National Anti-Corruption (NACC) calling for an investigation into what they believe to be malfeasance committed by Pol Col Tawee and DSI director-general Pol Maj Yutthana Praedam in connection with the Senate election probe.
The move followed the March 6 decision by the DSI's special cases board to investigate money-laundering allegations related to last year's multi-level Senate polls suspected to be fraught with collusion among some candidates.
The group alleged the DSI took up the probe despite having no authority to do so, said Sen Chatwat Saengpetch who led 80 other senators to submit the petition to the NACC on Wednesday.
They maintained the poll-related investigations fall within the jurisdiction of the Election Commission (EC).
Signed by 105 senators, the petition was received on Wednesday by NACC secretary-general Sarote Phuengramphan.
The motive behind the DSI's move was to level false accusations against the senators and see them legally penalised for crimes they did not commit, said Pol Maj Gen Chatwat.
He said the results of the Senate polls have been endorsed by the EC under Section 107 of the constitution.
As a former police investigator, Pol Maj Gen Chatwat said he was curious to know what evidence the DSI has to justify its investigation.
He also questioned why the DSI is pressing ahead even though it lacks the authority to do so. Its probe may also duplicate the work of the EC which is looking into the alleged election fraud, he noted.
Pol Maj Gen Chatwat said he believe the DSI's investigation is proof of the agency's exposure to political interference.
The senator also confirmed the Senate's anti-graft committee was in the middle of studying a proposal to dissolve the DSI.