SPRINGFIELD, Ill. (AP) — An Illinois state senator under federal investigation for fraud has resigned his office.

In a letter sent Wednesday to the secretary of the senate, Chicago Democrat Martin A. Sandoval said his resignation is effective Jan. 1.

FBI agents raided Sandoval’s Springfield and Chicago offices and home Sept. 24 seeking data on concrete and construction businesses, bribery or theft of federal funds.

After the raid, Gov. J.B. Pritzker and others demanded Sandoval step down as chairman of the Transportation Committee. Pritzker expressed concern about the integrity of his $41.5 billion state construction program, in which Sandoval took a leading role last spring.

Sandoval has represented the 11th District since 2003. In his letter, Sandoval said his respect for his constituents and the Senate convinced him that his resignation was necessary.