A Thai inquest into the death of a Japanese cameraman during a military crackdown five years ago against protesters ended inconclusively Thursday with the court unable to decide who fired the fatal shot.

Hiroyuki Muramoto, 43, of the Thomson Reuters news agency, was shot in the chest by an unknown gunman on April 10, 2010 while covering clashes between Thai troops and the anti-government Red Shirts

Some previous inquests into fatal cases linked to the violence have pointed the finger of blame at soldiers, including the killing of Italian photojournalist Fabio Polenghi.

In November 2011 the government of now ousted Prime Minister Yingluck Shinawatra said there was "clear" evidence that father of two Muramoto had also been felled by a soldier's rifle.

But Bangkok's Southern Criminal Court said it could not definitively say whether the Japanese journalist and two Red Shirt demonstrators killed nearby were shot by soldiers or armed protesters.

Currently Thailand is controlled by the military.

"It cannot be said who the shooters were or which direction the bullets came from," the judge said.

More than 90 people, mostly civilians, were killed and nearly 1,900 were injured in Thailand's worst political bloodshed in decades.

An inquest in 2013 ruled that six Thais taking shelter at a temple during the clashes, including a nurse and two rescue volunteers, were shot dead by military snipers shooting into the complex from Bangkok's elevated rail system.

No soldier or official has been prosecuted in connection with the deaths during the unrest, prompting anger from relatives and rights groups who say those responsible are being protected by a culture of impunity in Thailand.

Red Shirt leader Thida Thavornsert said she was unhappy with the latest decision.

"We are disappointed because there was another case in which two people died in the same area and the court at the time blamed the authorities," she told AFP.

Earlier this month the Red Shirts cancelled a religious ceremony marking the fifth anniversary of the crackdown, accusing security forces of surrounding a temple where the memorial was due to take place.

The Red Shirts are loyal to ousted premier Thaksin Shinawatra who was deposed in a 2006 military coup and later went into self-imposed exile.

In 2010 his supporters were protesting for fresh elections, a request that was eventually granted a year later bringing his sister Yingluck to power.

Her government was subsequently toppled last May following months of street protests and a military takeover.

It was the latest chapter in a decade of political conflict broadly pitting Bangkok's middle classes and the royalist elite -- backed by parts of the military and judiciary -- against pro-Shinawatra urban working-class voters and farmers from the country's north.

Coup leader and now Prime Minister Prayut Chan-O-Cha was one of the senior generals who oversaw the 2010 crackdown.