Five men accused of the shock murder of top Kremlin critic Boris Nemtsov last year faced the jury on Monday as their high-profile trial opened at a Russian military court. Nemtsov, a former deputy prime minister and one of the most prominent opposition politicians who openly criticized President Vladimir Putin, was gunned down late at night on February 27 last year as he walked across a bridge near the Kremlin. The suspects, all ethnic Chechens, sat in a glass cage in a Moscow courtroom packed with journalists, diplomats, rights activists. The men, who were guarded by police and special forces wearing balaclavas, all said they were pleading not guilty. The full trial opened after months of stalling as investigators hunted for Ruslan Mukhudinov, a low-ranking Chechen security official who they say paid the suspects to kill Nemtsov, although the motive is still unclear. Nemtsov's supporters argue that the probe did not question high-profile figures, such as Chechnya's fiercely Kremlin-loyal governor Ramzan Kadyrov, and never targeted those who ordered the murder in a high-traffic area that is closely watched by police. "The murder of Boris Nemtsov has not been solved," said lawyer Olga Mikhailova, who represents Nemtsov's family. "The organizer... has not been found and has not been brought to justice." The five defendants — Zaur Dadayev, Anzor Gubashev, Shadid Gubashev, Temirlan Eskerkhanov and Khamzat Bakhayev — are accused of involvement in the contract killing as an organized group and of illegal weapons trafficking. A preliminary hearing in July decided to put them on trial by jury, which was selected in August and September. Jury trials are relatively unusual in Russia and are only used for very serious offenses punishable by a life sentence. Prosecutors said the tight-knit group of suspects had watched Nemtsov since September 2014 and "carefully prepared a plan," acquiring two apartments, cars, the murder weapon and phones to discuss what they would do, after being offered 15 million rubles (about $240,000) for the murder. Mukhudinov, the man who allegedly offered them the money, has fled from Russia, according to investigators. Nemtsov, who at the time of murder was serving as a regional lawmaker in Yaroslavl, a city north of Moscow, was followed on the night of the murder as he was walking from a cafe on Red Square. Prosecutors say Dadayev shot at him six times, causing four fatal wounds, then jumped into a getaway car driven by Gubashev and drove off with the headlights off. The men left for Chechnya over the next two days, the prosecution said. Nemtsov's killing, the most high-profile murder in Russia's recent history, shook the country, where the opposition has been increasingly marginalized and smeared by state media. The politician was at the time of his killing probing Moscow's covert deployment of troops to Ukraine and had a running feud with Chechen strongman Kadyrov.