PROVIDENCE, R.I. — The political world in Rhode Island remained in turmoil on Sunday as two members of the State House scrambled for support to become the next speaker after the sudden resignation of Gordon D. Fox, a Democrat who had held the job since 2010.

Mr. Fox resigned on Saturday, and the reason remained a mystery. In a move that seemed designed to draw attention, several federal and state agents, including some from the Internal Revenue Service, raided his office in the House and his home on Friday and were seen carting out boxes and bags labeled “evidence.”

But no one has offered an explanation for the raid or said what the authorities were searching for, and Mr. Fox gave no clues in a statement he issued late Saturday announcing his resignation as speaker. Mr. Fox, 52, who was first elected to the State House of Representatives in 1992, also announced that he would not seek re-election this fall. He said he did intend to complete his current term, which ends in December.