Another suspect, Hambit Bintih, the incumbent chief of Gunung Mas District in Central Kalimantan, was arrested at a Jakarta hotel, Budi said.
The district chief was re-elected Sept. 4, but two competitors filed a lawsuit with the Constitutional Court alleging that Bintih paid voters. Mochtar was a member of the three-judge panel handling the case.
The nine-member Constitutional Court is as powerful as the Supreme Court and oversees cases reviewing constitutional law and disputes over elections and authority over state institutions.
Two other suspects were taken into custody later Thursday and 1 billion rupiah ($87,000) was seized in connection with another regional election in Banten province, Budi said, adding that the money was to be given to Mochtar.
President Susilo Bambang Yudhoyono expressed shock and questioned the integrity of previous court decisions.
"If the verdicts were wrong, the impact would be great because they are final and binding," he told a news conference.
Jimly Ashiddiqqie, a law professor at the University of Indonesia and the first head of the Constitutional Court, was outraged by the accusations and said the maximum penalty of life imprisonment was not enough for such crimes.
"We must be ruthless against unscrupulous criminals like this," he told local TVOne. "He deserves a death sentence."
In the other recent cases, the head of the country's oil and gas regulator was arrested on charges of receiving bribes worth up to $700,000 from a private oil company. The leader of the Islamic-based Prosperous Justice Party was also arrested on suspicion of accepting bribes to secure a government contract for a meat importer.
Endemic graft in Indonesia has been blamed for deterring foreign investment.