Alexander Taraikovsky, 34, died in the capital Minsk on Monday as unprecedented protests erupted.
Events in Belarus were sparked by Alexander Lukashenko – widely regarded as a dictator – who claimed victory in the contested presidential elections to continue his 26 years in power.
Protesters say Mr Taraikovsky was shot dead by police. But the Belarusian government said he was dead after an explosive device he intended to throw at officers exploded in his hand.
In images that have now emerged of Mr Taraikovsky’s death, the protester is shown with his hands on his body as blood flows from his chest amid the sounds of explosions and gunfire.
He then collapses in front of a line of riot police and stands still, before the officers march in line towards the body and some crowd him.
Police have fired tear gas, rubber bullets and stun grenades during weeklong protests since last Sunday’s elections.
After looking at the footage, Mr. Taraikovsky’s partner, Elena German, said: “He has nothing in his hand.
“Here’s a shot, they shoot, he grabs her chest. Some blood. He falls. “
Ms German, who was able to see Mr Taraikovsky’s body in a morgue on Friday, called on international experts to investigate the death of her partner.
“There is a seam in the chest – the hole was sewn up, but there is a black bruise; it’s small but we noticed it, ”she said.
“Her hands and feet are completely intact, there aren’t even any bruises. Obviously it was a bullet in the chest. ”
On Saturday, the day of Mr. Taraikovsky’s funeral, thousands of people gathered at the site where the car mechanic died.
Some protesters showed bruises which they claimed were due to police beatings.
Other demonstrations, within the framework of a huge “Freedom March”, are expected in Minsk.
The protest is scheduled to culminate in the city’s Independence Square outside the main government building.
There are fears of clashes because a pro-government rally is also planned.
The opposition claimed that Lukashenko was planning to transport people from other parts of the country by bus and that they were forced to participate.
Last Sunday’s elections were condemned internationally as unfair, while the Belarusian government was urged to end its use of violence in its attempts to quell the ongoing protests.
Meanwhile, Igor Lesgchenya – Belarusian Ambassador to Slovakia – has become the first diplomat from his country to support protests in his country.
In a video message, Mr. Lesgchenya said: “In Slovakia, I represent Belarus and the Belarusian people, who according to the constitution are the sole source of power in our country.
“I stand in solidarity with those who took to the streets of Belarusian cities with peaceful processions so that their voices could be heard. ”
He added: “I sincerely hope that the future of my country will be based on taking into account the positions of all sectors of society and representatives of various political forces.
“Belarusians have suffered this right. “
Protesters in Belarus are calling for the main opposition figure, Svetlana Tikhanovskaya, to be recognized as the winner of Sunday’s presidential election.
Mr Lukashenko was declared the winner with 80% of the vote, against only 10% for Ms Tikhanouskaya, who has now fled to Lithuania.
Ms. Tikhanouskaya stood for election alongside two other women; Maria Kolesnikova and Veronika Tsepkalo.
Ms Tikhanovskaya and Ms Tsepkalo entered the competition after their husbands were barred from standing for election.
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Valery Tsepkalo fled Belarus with his two sons for Russia last month and is now in Ukraine, from where he has condemned the “politically motivated” corruption charges against him.
In the early hours of Sunday, he claimed his wife and children had been detained for more than two hours on the Russian side of the Russian-Ukrainian border as they tried to reach him.
Meanwhile, Kolesnikova condemned Lukashenko’s decision to pick up Russian Vladimir Putin’s phone on Saturday.
The controversial Belarusian president said the Russian leader had promised to help him secure the country if necessary.
“He tried to ask Putin for help,” Ms. Koleniskova told Sky News.
“We don’t like it of course because our independent and sovereign Belarus is the main goal and we don’t like losing it just because of a president who wants to stay president here. “