Ekrem Imamoğlu, the Mayor of Istanbul, was one of more than 100 people, including other politicians, journalists and businessmen, detained as part of an investigation on Wednesday March 19th. .
Today, Sunday 23rd, Imamoğlu was formally arrested and charged with "establishing and managing a criminal organisation, taking bribes, extortion, unlawfully recording personal data and rigging a tender".
Prosecutors want to charge him with "aiding an armed terrorist organisation", but the Turkish court decided not to pursue this line at this point in time.
Imamoğlu is seen as one of Erdoğan's most formidable political rivals. He is the only person running in the CHP's presidential candidate selection which is being held today. CHP is the largest opposition party in Turkey.
A day before his detention, Istanbul University announced it was revoking Imamoğlu's degree due to alleged irregularities, a measure, which if upheld, would put his ability to run as president into doubt. According to the Turkish constitution, presidents must have completed higher education to hold office.
Opposition figures say the arrests are politically motivated. However, the Turkish Ministry of Justice has criticised those who link Erdoğan to the arrests, and insist on its judicial independence.
For the past four nights, thousands have taken to the streets across Turkey in largely peaceful demonstrations. Authorities have tried to stifle the street demonstrations with a four-day ban on all gatherings in Istanbul, which was extended to Ankara and Izmir as protests spread across the country. Since Thursday, riot police have repeatedly clashed with protesters and could be seen firing pepper gas and water cannons towards crowds of demonstrators. Turkish authorities said 343 people were arrested on Friday night, the third day of protests, across the country.