The inquest said it was unknown who fired the bullet and stopped short of outright blaming the military. Rights groups have repeatedly called for Thailand's government to hold the powerful army accountable for its part in the violence.
A Bangkok South Criminal Court judge said that the inquest into the death of 48-year-old Fabio Polenghi showed the fatal shot "was fired from the direction of security forces" who were mobilised to quash the demonstration in central Bangkok.
The findings were a stark reminder of a battle fought between the Red Shirt protesters and the government under then-Prime Minister Abhisit Vejjajiva, which led to at least 91 deaths during the two months of demonstrations on the streets of Bangkok in 2010, and of a political divide that remains in the country.
Polenghi was shot as he tried to take pictures of the army's assault on the Red Shirt encampment.
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Born in Italy in 1962, Polenghi had been a fashion photographer for many years but was transitioning to news.
Elisabetta Polenghi, 48, his younger sister, was among 13 witnesses who testified in the court case. She was accompanied by her mother and her elder sister to hear the court's order today.
"It was positive but it's not the solution," Elisabetta Polenghi said of the inquest's results. "The solution will come when the responsible will be asked to go out of their duty, away from position that can hurt people."