The IDF report in January, 2010 concluded that there was no airstrike, as Goldstone had asserted (against his own evidence!) and that the mill was only hit by a tank shell during active fighting.
Since then, the UN asserted that it had evidence of a 500 lb. bomb, and HRW released a video (apparently the UN video) of the El Bader mill taken a few weeks after Cast Lead that seemed to show this bomb sitting on the floor of the mill:
According to The Guardian, this was the front part of an MK82 aircraft dropped bomb and was found on the first floor.
Because of this new evidence, the IDF reopened its investigation as to whether there was any aerial bombing of the mill.
After months of exhaustive investigation, a new IDF report concludes that it was right all along, and that there was no bomb dropped on the flour mill:
141. The case of the el-Bader flour mill was discussed in the January 2010 Update. It concerns allegations that the mill had been targeted with precision weapons in the course of a pre-planned air strike, as part of a systemic destruction of industrial infrastructure and with the purpose of depriving the civilian population of Gaza of food supplies. The IDF investigation into the matter concluded instead that the mill was been struck by a tank shell in the course of active combat activities, in order to neutralize immediate threats to IDF forces.
142. Following the publication of the January 2010 Update, various news media stated in February 2010 that the U.N. was in possession of evidence that contradicted the findings of the IDF investigation. Specifically, it was reported that an unexploded IAF bomb was found in the mill, even though the command investigation had concluded there had been no aerial strike.65
143. Upon reviewing these reports, the MAG requested and received additional evidence from the U.N. and ordered the IAF to re-open its investigation of the incident. The MAG also initiated a meeting with U.N. representatives, who had visited the site of the mill, to discuss their findings. The follow-up investigation confirmed the earlier finding that the mill had not been targeted by the IAF in the course of a pre-planned attack. The new reports, photographs taken by U.N. officials, and video footage examined appeared inconsistent with an airborne strike, particularly given the absence of entry holes in the roof of the mill; the lack of trace marks on the floor where the shell was allegedly found (such trace marks would normally be expected when such a munition penetrates a building); and the fact that the fire which damaged the machinery in the mill broke out on the second floor while the ordnance was found on the first floor.
144. Furthermore, the IAF examined every aerial attack in the vicinity of the mill in the course of the Gaza Operation and found that none of them could have resulted in a hit on the flour mill. Of the seven strikes conducted within a one-kilometer radius of the mill using the particular munitions identified, five had hit their precise target (the closest one being approximately 300 meters away from the mill). The impact sites of the two additional strikes were visible in the IAF aerial footage of the operation, and the closer of the two landed a full 350 meters from the mill.
145. After reviewing the findings of this additional investigation, the MAG could not affirmatively determine how the ordnance had found its way into the mill, but reaffirmed that the flour mill had not been intentionally targeted by the IAF. He was also unable to rule out the possibility that the ordnance had been deliberately planted in the mill. Accordingly, the MAG determined that there was no basis for additional proceedings in this matter.
It is noteworthy that the HRW/UN video shows no holes in the roof of the mill; the only hole is a relatively small one shown here on the side:
How exactly a 500 lb bomb could make it through this relatively small hole and end up on the first floor, without any pictures of a large hole in the floor, did not seem to occur to the UN, HRW or the Guardian.
Although the IDF is loathe to directly say that the bomb was planted there, it sure looks like that is what happened. And if evidence was tampered with here, who knows what other evidence was planted in the weeks after the war for the credulous reporters and NGOs that descended on Gaza to look for proof of war crimes?