The US-based cleric who has emerged as the arch foe of Turkish President Recep Tayyip Erdogan goes on trial with dozens of former police officers on Wednesday over the publication in 2013 of graft claims that rocked Turkey's strongman. The trial at Istanbul's main courthouse is part of a crackdown against the movement of cleric Fethullah Gulen, which the government describes as a battle against a "parallel state" but opponents say amounts to repression of critics. Gulen, 74, was an ally of Erdogan when his Islamic-rooted Justice and Development Party (AKP) came to power in 2002. But the two fell out as Gulen's own influence increased and the government blamed his movement for the stunning corruption allegations against Erdogan's inner circle, including his own son Bilal, that broke in December 2013. Gulen, who lives in exile in a secluded compound in the US state of Pennsylvania, will be tried in absentia. He stands charged of "attempting to bring down the government" and "running a terrorist group," his lawyer Nurullah Albayrak said. Gulen is accused of giving orders to allies in Turkey's police force to launch the probe. But Albayrak said that the evidence offered by the prosecutors in the 1,453 page-long indictment failed to support these claims. "There is no evidence that this was a terrorist organization. The charges are based on assumptions and on simple declarations and these are not enough," he said. "The only proof they have is a single phone call made by my client (Gulen) to a police officer the day the scandal broke, and in that one, there is no indication that he is giving orders to anyone." Prosecutors are seeking an aggravated life term — the highest penalty possible in Turkey — for Gulen and two former police chiefs. The other 66 suspects in the case, most of them police officers charged with being members of an armed organization, face jail time ranging from seven years to 330 years. Gulen is currently being investigated in two other cases but Wednesday's trial is the most high-profile as it directly concerns the corruption scandal, which posed one of the biggest challenges to Erdogan in his career first as premier and now as president. Gulen has been based in the United States since 1999 when he fled charges against him laid by the former secular authorities. Turkey has asked the United States to extradite him but Washington has shown little appetite for doing so. Despite living outside of Turkey, Gulen built up huge influence in the country through allies in the police and judiciary, media and financial interests and a vast network of cramming schools designed to make up for deficiencies in the state education system. Ankara now accuses Gulen of running what it calls the Fethullahaci Terror Organization/Parallel State Structure (FeTO/PDY) and seeking to overthrow the legitimate Turkish authorities. Gulen supporters decry the accusations as ridiculous, saying all he leads is a more informal group known as Hizmet (Service). The authorities have in the last months stepped up investigations into companies with ties to Gulen, including a series of raids on pro-Gulen media that have raised fears about the government's commitment to democracy. According to the state-run Anatolia news agency, around 1,800 people, including 750 police officers and 80 soldiers, have been detained as part of a crackdown against the followers of Gulen since arrests began in the summer 2014. Some 280 of them are still in jail pending trial, Anatolia said. Supporters of Gulen are currently being investigated over a number of controversial cases including the interception of trucks belonging to Turkey's secret service allegedly carrying arms bound for Syria, as well as illegal eavesdropping of top officials including Erdogan. "We promise that the gang leaders and others will be brought to justice," Erdogan said late last month.