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.

The corruption watchdog, Transparency International, slammed the prosecutors’ decision to drop the case saying the move “calls into question the rule of law in Turkey.”

‘These are serious allegations and Turkish people need to see that there is a transparent judicial process that shows there is no impunity for people in power,” said Oya Ozarslan who heads Transparency International in Turkey. “The failure to complete the case is a bad signal for the fight against corruption.”

The government had rejected the corruption allegations, insisting the probes against Erdogan’s allies and son were orchestrated by followers of an influential U.S.-based Muslim cleric in a bid to topple the government.

Erdogan’s government immediately moved to replace prosecutors and police investigating the probe and dozens of police officers have been detained across Turkey on suspicion of illegal wiretaps.

Erdogan, who was prime minister at the time, won local elections in March and presidential elections in August despite the corruption allegations.