The state Senate has spent $9,000 to hire a law firm it has used before to investigate sexual-harassment complaints, according to records in Comptroller Thomas DiNapoli’s office.

Senate officials won’t say why it rehired Kraus & Zuchlewski LLP last month, citing confidentiality covering personnel matters.

Democratic state Sen. Marc Panepinto of Buffalo announced this year he would not seek re-election after reports surfaced that police were investigating underage drinking at his home while he and his wife were away.

Panepinto has repeatedly declined to comment.

One Senate source said the law firm’s hiring doesn’t mean charges will be brought.