Turkish prosecutors are laying the groundwork for large-scale trials of hundreds of people accused of participating in a coup attempt last July, an undertaking that is already transforming society and will be a reckoning of sorts for a nation that has endured much upheaval in recent years.

Authorities say the trials will shed light on alleged links between the accused and Fethullah Gülen, an exiled US-based preacher with a vast grassroots network.

The onset of the trials has refocused attention on the large-scale purges of Turkey’s government, media and academia after the coup attempt, in which tens of thousands of people – many with no known links to the Gülenists – were dismissed or jailed.

Meanwhile, Turkey is preparing for a referendum on Sunday on greater presidential powers, which could prove the most significant political development in the history of the republic.

“What happened on 15 July [the day of the attempted coup] and what is now happening for months is completely transformative for Turkey,” said a journalist who worked for a Gülen-affiliated media outlet and requested anonymity for fear of reprisals. “One big part of society has been subjected to extreme demonisation in a process that cost them their jobs, reputation, freedom or ultimately their lives. Another part of the society has been filled with anger and radically politicised.



“Nothing can be the same as before 15 July any longer – ever,” he added.

Turkish courts have already begun several parallel trials over the coup attempt. Last month prosecutors demanded life sentences for 47 people accused of attempting to assassinate the president, Recep Tayyip Erdoğan, on the night of the putsch, and the largest trial yet opened on 28 February in a specially built courtroom outside Ankara filled with more than 300 suspects accused of murder and attempting to overthrow the government.

About 270 suspects, including Gülen, went on trial in absentia in Izmir in January, and an indictment issued in late February alleges that Gülenists infiltrated the state and charges 31 members of the military with attempting to overthrow the constitutional order.

The state intelligence agency, the National Intelligence Service (MIT), has sent prosecutors in Ankara a list of 122,000 individuals who allegedly used a secure messaging app, ByLock, which security officials say was widely used by the Gülen network for communications.

The sheer number of those swept up by the government’s campaign has prompted criticism of Turkey by its allies in the west, who accuse it of going far beyond the Gülen network and targeting dissidents who oppose the ruling party and the president.

People gather around police officers loyal to the government standing atop tanks abandoned on the Bosphorus Bridge after the coup attempt. Photograph: Emrah Gurel/AP

The trials will transform a political scene in Turkey still reeling from the break in relations between Erdoğan and Gülen, who were allies for the first decade of AK party rule.

Ankara has demanded Gülen’s extradition from the US and few in opposition or government circles dispute the Gülenists’ involvement in the coup attempt, yet the government has publicly presented little evidence.

So far, the known evidence includes the testimony of Gen Hulusi Akar, chief of staff of the armed forces, who was detained on the night of the coup attempt. Turkey’s most senior soldier said the rebels offered to put him on the phone with Gülen in an effort to convince him to join their cause.

Another piece of evidence is the alleged whereabouts of Adil Öksüz, an imam whom Turkish prosecutors accuse of being part of the Gülen movement. Öksüz reportedly travelled to the US days before the coup attempt to meet the reclusive preacher, and on the night of the attempt was seen at Ankara’s Akıncı airbase. He was detained briefly and then released by officers, many of whom were subsequently arrested. Öksüz remains at large.

Key defendants in the trials have strongly denied having any links with the Gülen movement. Gen Gokhan Sonmezates, one of the highest-ranking generals on trial for allegedly attempting to assassinate Erdoğan, said he had no links to the movement and had taken part in the attempted putsch to end “domestic decay” and corruption as well as the threat posed by Kurdish militants.

Alongside the trials, a key part of the attempt to dismantle the network is the efforts of the Turkish intelligence service to identify alleged members through ByLock, which officials say was the primary means of communication by Gülenists between 2013 and 2015.

MIT has deciphered 18m messages, some of which have been seen by the Guardian and which appear to shed new light on the network, its infiltration of the state apparatus and the challenges it faced after Gülen fell out with Erdoğan.

Fethullah Gülen. Photograph: Chris Post/AP

The message intercepts do not incriminate the Gülenists, who stopped using ByLock six months before the coup attempt, apparently because they realised its security had been compromised by the state. The messages seen by the Guardian were only a small sample of the total, and some had been redacted to obscure specific names and phone numbers as well as “operational details”. The Guardian could not independently verify their authenticity.

The messages appear to show how members of the group had forewarning of police raids targeting Gülen-linked financial and media institutions, apparently from sources inside the bureaucracy; how the group extracted funds from its followers; and how it suffered financially during a government crackdown, growing increasingly desperate for donations.

They offer glimpses of the high regard in which members of the movement hold Gülen. They include apocryphal stories used to raise the spirits of the movement’s members amid the crackdown.

In one conversation from August 2015, participants discuss a lawsuit that may implicate members of the movement who allegedly fabricated signatures and evidence in a wide-ranging investigation that accused senior military officers as well as journalists of plotting to overthrow the government. They also discuss a potential crackdown on the group ordered by Erdoğan, who is referred to as “the tyrant”.

In mid-August the group grows increasingly certain that the crackdown will occur, sending out instructions to lawyers to carefully monitor any takeovers by the government. The following week, tips are circulated on how to wipe hard drives clean of any data.

A week after that message, the Turkish government seized Ipek Holding, an organisation with alleged Gülenist ties, appointing a trustee board to manage its affairs and closing down its media outlets.

Messages circulated on the network also discuss the appointments of new prosecutors, identifying who among them is anti-Gülenist, as well as appointments of new police officials after the dismissal of Gülenist officers.

In October 2015, participants in the network discuss an upcoming raid on 69 branches of Bank Asya, widely believed to have been founded by the Gülen group and which was seized by the government that year.

The message warning against the raids is striking in its detail, saying the raid order comes from the smuggling and organised crime unit within the police and has been sent to 69 police directorates around the country. It also offers details of the suspected financial irregularities investigators will be looking for, including fake signatures on transactions, transfers from the accounts of teachers affiliated with the Gülen movement into the group’s bank accounts, and regular contributions to the movement by bank workers. The message warns that bank employees will be interrogated by the investigators.

The ongoing trials will force Turkey to come to terms with the scale of the upheaval that followed the coup attempt, and the wholesale reorganisation of society in the crackdown’s aftermath.

“It’s called civil death,” said a university professor with a long history of leftist activism and opposition to the Gülenists, but who nevertheless was dismissed from his post after the coup attempt. “The rule of law is in ruins. You’re accused until proven innocent.”

The professor has been banned from working in universities in the country, and lost his pension and his academic passport.

Asked how Turkish society would be altered by the crackdown, he said he had no easy answer. “This isn’t the country I knew. This is a new Turkey that I don’t know, and it’s getting worse day by day. We are losing our democratic rights, rule of law. Arbitrary measures are regular.”