By Joe Bavier KINSHASA, March 7 (Reuters) - The United Nations has sharply criticised as inadequate a Congolese military investigation and murder trial which followed the killing of a U.N. radio journalist by armed men in military uniform last June. Serge Maheshe was shot in the legs and chest by two men on June 13 as he was leaving a friend's home in the eastern town of Bukavu, where he was editor-in-chief of U.N.-backed Okapi radio, a station set up to help bolster the country's peace process. A military court in August sentenced to death four people for the crime, two demobilised soldiers and two of Maheshe's close friends, Serge Muhima and Alain Mulimbi, who were convicted of ordering the killing. All have appealed. "The observation of the trial demonstrated that not only was there no real criminal investigation, but that neither the public prosecutor nor the military tribunal genuinely sought to establish the truth," U.N. human rights observers said in a report published on Thursday. Congo's top military justice official General Joseph Ponde refused a telephone interview with Reuters and there was no immediate official reaction to the report. The report questioned the military tribunal's jurisdiction, as all four accused were civilians at the time of the killing, and denounced the fact that no autopsy had been carried out and that a U.N. offer to assist in ballistics analysis of the alleged murder weapon was turned down. "This ballistics expertise would have permitted the verification that this weapon was in a state to function and shoot, which was doubtful given the advanced state of disrepair of this rusty weapon," the report said. PROCESS RUSHED THROUGH In a letter to the head of the military court on Sept. 8, the two convicted assassins retracted their testimony against Muhima and Mulimbi. They said they had been pressured by two military magistrates to implicate Maheshe's friends. U.N. efforts to bring the letter to the attention of Congo's top military justice officials were met with a "total absence of reaction", the report said. The trial before the military tribunal began just hours after Maheshe's murder, sparking criticism from rights campaigners that the process was being rushed through. A day after Mulimbi and Muhima's conviction, international press watchdog Reporters without Borders (RSF), called the decision "stupefying" and accused Congolese authorities of condemning two innocent men to death. "This was not only a grave miscarriage of justice but a deliberate cover-up," a senior researcher with New York-based Human Rights Watch Anneke Van Woudenberg told Reuters. "At no time did the investigation attempt to look at other people possibly responsible for the crime, despite strong evidence against government soldiers." In the months leading up to his murder, Maheshe told human rights activists that he had received death threats from the elite Republican Guard, a lead which the U.N. report said investigators should have followed up more closely. Threats and intimidation against journalists are common in Democratic Republic of Congo, which in 2006 held its first free elections in more than four decades. At least four journalists have been killed since 2005 in the vast former Belgian colony. (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/ ) (Editing by Nick Tattersall)