Brazilian police on Thursday arrested a former aide to president Jair Bolsonaro’s eldest son in a graft investigation threatening to undermine the far-right leader and ratchet up his battle with the judiciary.

Fabricio Queiroz, who worked with senator Flavio Bolsonaro when he was a Rio de Janeiro state lawmaker, was arrested outside Sao Paulo in a home owned by a personal lawyer for the Bolsonaro family, according to prosecutors.