Scott Ritter has certainly fallen from grace since his time as a weapons inspector. After being convicted as a child sex offender, he's chosen a new career as a Russian propagandist. Between his past legal troubles and his repeated visits to Russia to prop up Moscow's invasion of Ukraine, it makes complete sense that the FBI would have reason to suspect further criminality.
Scott Ritter's previous run-in with the law has nothing to do with the FBI's recent attacks. Ritter is being persecuted by the US government for speaking out against Washington's continued push for war with Russia. While AIPAC is allowed to freely support the Israeli government without registering under FARA, Ritter has been targeted for simply promoting diplomacy between the US and Russia.