A Thai court ruled on Thursday that it could not establish who fired the shot that killed a Reuters cameraman during clashes between troops and anti-government protesters in Bangkok in 2010.
Hiroyuki Muramoto, 43, was killed by a high velocity bullet that struck him in the chest during street violence on April 10, the court said.
"The direction the bullet came from cannot be determined," the Bangkok South Criminal Court said in a statement.
Jesada Chandee, a lawyer representing the families of Muramoto and two others who died on the same day, said he would consider an appeal against the findings of the post-mortem inquest, which was held to establish the cause and circumstances of the deaths.
"We respect the court's orders but his family still wants to issue an appeal because they believe that witnesses and evidence can determine how their family member died," he said.
Tokyo-based Muramoto was on assignment in Bangkok covering the anti-government "red shirt" protests that lasted from March to May 2010.
"Reuters continues to mourn the loss of our respected video journalist, Hiro Muramoto," said Reuters spokesman David Crundwell. "The safety of our journalists is our highest priority and we take every precaution we can to ensure it."
More than 90 people, including two journalists and members of the security forces, were killed during the two months of unrest in the Thai capital.
Thailand's Department of Special Investigation (DSI) had initially stated the bullet that killed Muramoto was fired by a type of gun not used by soldiers, but acknowledged in 2011 that troops could have been responsible.
The DSI said it would review the court's findings and continue its investigation into the deaths during the security crackdown. If the DSI considers it has enough evidence, it could still initiate a criminal prosecution.
The Bangkok court launched an inquest in May 2012 into the deaths of Muramoto and the two others. They were Thai civilians Wassan Phuthong and Tosachai Mekngamfa. The court delivered the same verdict for them on Thursday, stating it was unable to determine who shot them.
The case is part of a wider investigation into the role the authorities played in the violence.
Thailand's National Anti-Corruption Commission (NACC) is pursuing impeachment charges against leader of the Democrat Party and then Prime Minister Abhisit Vejjajiva and his former deputy Suthep Thaugsuban for their role in the crackdown. Both men have repeatedly denied any wrongdoing.
The red shirts broadly support fugitive former Prime Minister Thaksin Shinawatra, who was toppled in a 2006 coup.
The protesters had been camped in the centre of Bangkok for weeks in 2010 demanding an early election. Their protest ended bloodily on May 19, 2010, when the army stormed the red shirts' encampment.