ANKARA, Turkey (AP) — Turkish prosecutors dropped a bribery and corruption investigation that forced four government ministers to step down earlier in the year, drawing criticism on Saturday from an international graft watchdog which said the case should have been followed through to counter allegations that powerful politicians are able to act with impunity.

Prosecutors in Istanbul ruled Friday that there were no grounds for legal action against 53 suspects, including the sons of two former government ministers and a prominent Iranian businessman, who were suspected of bribery and corruption in a case that shook the country in December, the state-run Anadolu Agency reported. A separate investigation, involving President Recep Tayyip Erdogan’s son, was similarly dismissed in September.