For Oswald to be guilty he has to make the trip from the 6th floor "shooter's nest" to 2nd floor lunch room before Truly and Baker arrive there.
The only path for him to have done so was the rear staircase. (Truly's observation of the lifts precludes their use by Oswald)
Whilst the investigation proved the trip was possible in the time available, it did not prove the path was clear for him to have done so.
All staff in the TSBD between the 6th and 2nd should have been interviewed as to their location and if their actions could have precluded the suspect from using that route.
Adams and Styles descent time is controverted, however the obvious step was to interview Garner and Dorman. If the "Stroud" document is genuine (as I believe it is) then it would appear that the investigation did at least speak to Garner, got an answer they didn't like, so "lost" her testimony. Now Garner may have followed Adams and Styles as they made an early descent and then stayed in the rear area and saw Truly and Baker ascend, but that doesn't preclude Oswald somehow sneaking past her. However due to the failure of the investigation to properly check the possible people that may have been in Oswald's path and enter their testimony into the official record, we will never know officially iof the path was clear and that alone for me is reasonable doubt as to Oswald's guilt. (Especially when added to the fact that the investigation appears to have known about Garner's movements but appears to have deliberately excluded this piece of information)