Info from Wiki:
Following the death of Hammarskjöld, there were three inquiries into the circumstances that led to the crash: the Rhodesian Board of Investigation, the Rhodesian Commission of Inquiry, and the United Nations Commission of Investigation.[9]
The Rhodesian Board of Investigation looked into the matter between 19 September 1961 and 2 November 1961[9] under the command of British Lt. Colonel M.C.B. Barber. The Rhodesian Commission of Inquiry held hearings from 16–29 January 1962 without United Nations oversight. The subsequent United Nations Commission of Investigation held a series of hearings in 1962 and in part depended upon the testimony from the previous Rhodesian inquiries.[9] Five “eminent persons” were assigned by the new secretary-general to the UN Commission. The members of the commission unanimously elected Nepalese diplomat Rishikesh Shaha to head an inquiry.[9]
The three official inquiries failed to determine conclusively the cause of the crash that led to the death of Hammarskjöld. The Rhodesian Board of Investigation sent 180 men to search a six-square-kilometer area of the last sector of the aircraft’s flight path, looking for evidence as to the cause of the crash. No evidence of a bomb, surface-to-air missile, or hijacking was found. The official report stated that two of the dead Swedish bodyguards had suffered multiple bullet wounds. Medical examination, performed by the initial Rhodesian Board of Investigation and reported in the UN official report, indicated that the wounds were superficial, and that the bullets showed no signs of rifling. They concluded that cartridges had exploded in the fire in proximity to the bodyguards.[9] No evidence of foul play was found in the wreckage of the aircraft.[10]
Previous accounts of a bright flash in the sky were dismissed as occurring too late in the evening to have caused the crash. The UN report speculated that these flashes may have been caused by secondary explosions after the crash. Sergeant Harold Julien, who initially survived the crash but died days later,[11] indicated that there was a series of explosions that preceded the crash.[9][12] The official inquiry found that the statements of witnesses who talked with Julien before he died in hospital five days after the crash[13] were inconsistent.
The report states that there were numerous delays that violated established search and rescue procedures. There were three separate delays: the first delayed the initial alarm of a possible plane in trouble; the second delayed the “distress” alarm, which indicates that communications with surrounding airports indicate that a missing plane has not landed elsewhere; the third delayed the eventual search and rescue operation and the discovery of the plane wreckage, just miles away. The medical examiner’s report was inconclusive; one report said that Hammarskjöld had died on impact; another stated that Hammarskjöld might have survived had rescue operations not been delayed.[9] The report also said that the chances of Sgt. Julien surviving the crash would have been “infinitely” better if the rescue operations had been hastened.[9]
On 16 March 2015, UN Secretary General Ban Ki-moon appointed members to an independent panel of experts to examine new information related to the tragedy. The three-member panel was led by Mohamed Chande Othman, the Chief Justice of Tanzania. The other two members were Kerryn Macaulay (Australia’s representative to ICAO) and Henrik Larsen (a ballistics expert from the Danish National Police). The report was handed over to the secretary-general on 12 June 2015.[14]
Bullets in a fire tend to stay put or move slightly…because they are lead and heavy. while the cases, which are light tend to fly off but with not enough mass to penetrate very far.