Return to the Senate (1998–2010)
In 1998, Pimentel ran successfully for another term in the Senate of the Philippines, from 1998 to 2004. Along with Edgardo Angara and Juan Ponce Enrile, Pimentel is one of the three senators elected in 1987 to return to the Senate.
In May 2003, Pimentel and congresswoman Etta Rosales filed a petition before the Supreme Court to compel the executive branch in transmitting the Rome Statute to the Senate in order to ratify the Philippines' membership in the International Criminal Court; it was later dismissed in July 2005.
He was re-elected in the May 10, 2004 national elections, attaining the third-highest number of votes of nearly 80 candidates for the 12 Senate seats.
During his term at the Senate, Pimentel authored several bills and resolutions, some of which have already been enacted into law:
R.A. No.7160, The Local Government Code in 1991
R.A. No. 6938, The Cooperative Code
R.A. No. 6678, The Generic Drugs Act
R.A. No. 6734, An Act Creating the Autonomous Region in Muslim Mindanao
In October 2000, Senate President Franklin Drilon issued a statement about the Juetengate scandal of President Joseph Estrada. Drilon was removed as Senate President the next month through a Senate revamp and Pimentel was installed as Senate President. In December 2000, an impeachment case was filed on the Senate. On January 16, 2001, Pimentel was one of those who voted in favor of the opening of the second bank envelope. Their vote was outnumbered and some of the opposition senators cried in front of Senate President Pimentel. Joseph Estrada was ousted in January by the second EDSA People Power Revolution, but he was pardoned by his successor, Gloria Macapagal Arroyo on October 26, 2007. Pimentel occupied the Senate presidency until the end of the regular session in June 2001. As he explained his vote to open he declared: I vote to do so because that is the only way to determine whether or not the contents of the envelope are relevant or material to the case at bar. Because of this development, Mr. Chief Justice, I realize that the NO’s have it. And therefore, I resign my presidency of the Senate as soon as my successor is elected.
Before stepping down as senator, Pimentel made a final privilege speech, where he demanded the American government and the Field Museum of Natural History in Chicago to return to the Philippines the Golden Tara, one of the most significant artifacts in the entire country which landed in American possession during the financial crisis in the Philippines.
As chair of the Blue Ribbon Committee, he has recommended the prosecution of top government officials of previous administrations in relation to the Expo Pilipino centennial scam and the misuse of the funds of the Retirement and Separation Benefits Systems of the Armed Forces. He has also recommended the prosecution of certain personnel of the Land Registration Administration for involvement in faking of land titles. Recently his committee also conducted series of investigations into the allegation of Governor Luis "Chavit" Singson on jueteng scandal. As Chair of the Committee on Local Government, he has supported far-reaching amendments to further strengthen the role of local government units in national development. He has also gotten senate approval to return the police to the supervision of LGUs and has authored a law to fix the date for elections of ARMM officials.
He was the president and founder of the PDP–Laban party. On April 25, 2008, Senator Pimentel authored a bill that would shift the Philippines into a Federal Republic of the Philippines.
