On the surface, the case against Chelakh appeared strong. Days after the killings in May at a remote outpost along the Chinese border, Chelakh was found hiding in a cave, wearing civilian clothes and carrying a pistol. Authorities said Chelakh soon confessed.
But many people in the tightly governed former Soviet Central Asian nation were skeptical, contending in online forums that the 19-year-old had been forced to claim the crime. In a dramatic demonstration of mistrust of the authorities, a newsreader at a private television station quit rather than report about Chelakh's confession.
"Can any journalist or newsreader seriously read out this news on air? It's a disgrace!" the anchor, Vladislav Dlinnov, wrote on his Twitter account at the time.
The widespread disbelief appears to reflect simmering resentment in a nation with few outlets for expressing opposition. Those questioning the verdict didn't cite any evidence of their own.
"The explanation of what happened at the outpost is most likely that contained in Chelakh's own confession," said political observer Petr Svoik. "But the public is operating on the basis that if the authorities have suggested a scenario, it likely isn't true."
The mistrust could be corrosive to a country that has mostly avoided the strife that plagued many other former Soviet states and that has won plaudits for tolerance among its many ethnic groups. But Kazakhstan's placidity has been troubled recently, as witnessed by an unprecedented wave of shootings blamed on Islamic radicals over the past two years.
"This is a serious strain that will spread disappointment and discontent in society," said Guljan Yergalieva, a vocal opposition figure.
Her muckraking website cited unidentified sources as saying investigators had linked the killings to a top security official with family ties to President Nursultan Nazarbayev, who thoroughly dominates Kazakh politics.
Even relatives of the victims initially greeted the news of Chelakh's confession with disbelief and were only persuaded of the defendant's guilt by evidence laid out during the three-week trial, including the prosecution's three videos of Chelakh.
"When we came to court in the beginning, we didn't entirely believe what had happened, but now we have seen everything with our own eyes," Sagyndyk Yemenov, the father of one of the murdered guards, told The Associated Press outside the court in Taldykorgan, 225 kilometers (140 miles) north of Almaty, Kazakhstan's principal city.
In a videotaped confession to investigators that also surfaced online, Chelakh explains how he took a Makarov pistol and automatic rifles from the weapons storage room at the post and killed a fellow guard on sentry duty. In a reconstruction of his movements filmed at the site of the killings, Chelakh uses a wooden rifle to show how he then mowed down all the remaining guards.
He says that he walked to the cabin of a local park ranger, whom he killed to get rid of a potential witness to the crime scene.
Skeptics claimed the video was doctored, with sections cut from it before being shown at the trial.
In another video, Chelakh appears to lend weight to the theory that he was motivated by revenge for sustained mistreatment by his colleagues. "During all the time at the frontier post, they demeaned and insulted me," he said.
Chelakh subsequently retracted this confession, attributing the killings to unidentified attackers.
The trial saw scenes that veered between the tragic and the absurd, putting the credibility of the whole process under severe strain.
Defense lawyer Serik Sarsenov caused consternation when he announced to reporters in the opening days of the trial that information would emerge showing 18 bodies had been found, not 15 as claimed. Sarsenov never produced that evidence and then took to not showing up at hearings for days on end, citing unspecified health issues.
On one occasion, Chelakh, who had made vocal and angry demands not to be brought to the courtroom, snapped a fragment of chipboard off the bench in the defendants' glass case and abortively attempted to self-mutilate.
In what turned out to be the main plank of the prosecution's case, secretly filmed video footage was produced in which Chelakh was heard bragging to a cellmate about how he had picked off victims, who he said pleaded to be spared.
But Chelakh's mother, Svetlana Vaschenko, who has resolutely attended the entire trial in a cramped courtroom alongside the victims' family members, dismissed the footage as a crude forgery.
Chelakh successfully asked not to attend most of his trial, but was made to be present on the closing day. Court guards forced the defendant to face forward, prompting him to bite, kick out, swear and shout. As the prosecutor made his final statement, Chelakh could be heard sobbing.
Speculation about possible alternative scenarios involved an attack by smugglers on the outpost, which lies very close to the thinly protected border with China, or religious extremists.
Despite the occasional political scandal, Kazakhstan has succeeded in perpetuating stability by fostering a broad consensus on cautious economic development. But while the violation of democratic freedoms and media rights rarely inspires passions among the largely politically apathetic population, perceptions of malfeasance in the sensitive area of security create considerable unease.