Labour Day celebrations on Taksim Square in 1977 had seen the participation of well over 500,000 citizens. Many workers had not even entered the square when shots were heard. Most witnesses stated that they came from the building of the water supply company (Sular Idaresi) and the Intercontinental Hotel (now called The Marmara). Subsequently the security forces intervened with armoured vehicles making much noise with their sirens and explosives. They also hosed the crowd with pressurized water. Most casualties were caused by the panic that this attack created.

The figures regarding the casualties is still a debated issue, although the accredited numbers are of 37 persons killed and over 200 persons being injured.

On the day of the incident, Istanbul Radio Station announced that 34 people had been killed and 126 persons had been injured. According to the autopsy reports only four victims had been killed by bullets. In three cases the cause of death could either be a bullet or injuries to the head and 27 victims had been crushed. Several witnesses stated that Meral Özkol had been overrun by an armoured vehicle.

After the attack, over 500 demonstrators were detained, and 98 were indicted. Among the 17 defendants, who had been put in pre-trial detention, three were released before the first hearing and nine were released at the first hearing on 7 July 1977. The remaining prisoners were released soon afterwards. The trial ended in acquittal on 20 October 1989. Various sources stated that from the roof of the Water Supply Company, some 20 snipers were detained by the gendarmerie and handed over to the police. However, none of them appeared in the records of the police. This information comes from the prosecutor investigating the Taksim Square Massacre, Çetin Yetkin. He said that Lieutenant Abdullah Erim made the detentions and handed the detainees over to the police officers Muhsin Bodur and Mete Altan (who after the military coupon 12 September 1980 worked in the political department of Istanbul Police HQ). Both officers rejected the claim that they had been involved. It is nevertheless known that counter guerrilla forces prepared the attack on the crowd.

After three months of investigation, the prosecutor Çetin Yetkin was appointed elsewhere and resigned. Çetin Yetkin claimed that a sack with explosives had been handed over to the police, but later disappeared. Similarly the lawyer Rasim Öz alleged that he had shot a film of the incident showing many things including the snipers on the roof of the Water Supply Company. He had handed it over to the prosecutor's office, but it had been lost at Istanbul Police HQ.