As the year draws to a close, the Kremlin continues to insist that not a single Russian soldier has entered Ukraine to join the pro-Moscow separatist militia who have been fighting government forces since April.
This month, Vladimir Putin, the President, said that all Russian combatants in Ukraine's Donbas region were volunteer militiamen answering "a call of the heart".
The story of Tumanov and the shadowy deaths of scores of other Russian servicemen since the northern summer belie that claim.
Rights activists have recorded cases of at least 40 serving soldiers suspected of dying in the conflict, and many believe the figure is in the hundreds, but prosecutors refuse to investigate their deaths.
Denied any legal status by the lies and obfuscation that muffle their stories, these men and their families have been left in limbo. They are casualties of an undeclared war.
Officially, Tumanov died while "carrying out responsibilities of military service" at an unnamed "point of temporary deployment of military unit 27777", part of the army's 18th Guards Motor Rifle Brigade, whose permanent base is in Kalinovskaya, Chechnya. His death certificate records that he died from an "explosion injury", receiving "multiple shrapnel wounds to the lower limbs" that resulted in "acute, massive blood loss". The certificate leaves unticked a box saying the cause of his injuries was "military hostilities", preferring instead "origin not established".
Tumanova spoke to a major in Chechnya by telephone who confirmed her son had perished in Ukraine, but refused to explain why he was sent there or give any details.
Tumanov had served as a conscript soldier after school and he decided to return to the forces as a career soldier when he couldn't find a job. In June he was sent to Chechnya where, within 10 days, he and other soldiers at the base were approached and asked if they would go to Donbas to fight as volunteers.
He and his friends refused, he told his mother by telephone. "Who wants to die?" she said. "That was their thinking. Nobody was attacking Russia; if they had been, Anton would have been first in the queue."
By the middle of July, things had changed. Now 27777, his regular army unit, was dispatched to a temporary camp in the Rostov region, near the border with Ukraine, officially "for exercises". Soon he was telling Nastya Chernova, his fiancee, that he was going on short trips into Ukraine to accompany deliveries of arms and military vehicles to the rebels.
This was the moment when pro-Moscow militia in eastern Ukraine were on the brink of caving in to government forces, who had almost surrounded the separatist capital, Donetsk. Over the next month, Russia would stage a major intervention, sending tanks and troops across the border to help reclaim rebel territory.
On August 10, Tumanov telephoned his mother and said: "Tomorrow they are sending us to Donetsk [the rebel capital]. We're going to help the militia."
The next day he told her: "We're handing in our documents and our phones. They've given us two grenades and 150 rounds of ammunition each."
Tumanova knows what happened next from one of her son's comrades but she is still waiting for an explanation. She asked state prosecutors via a civil rights group to investigate her son's last days but there has been no reply.
At the town's military commissariat, employees said they had no information about Tumanov. A senior official at the medical centre in Rostov where his death was recorded also refused to comment.
"For me, what's important is that our Government doesn't hide what happened," said Tumanova. "Our children are nameless. If they sent our soldiers there, let them admit it. It's too late to bring Anton back but this is just inhuman."
