The Warren Report not only concluded that he was, but also that he had time to appear on the 2nd floor in 90 seconds.
If Oswald did, he would have had to go the length of the 6th floor to reach the stairwell.
He also would need time to stash a rifle behind boxes near the stairwell.
He, then, would go down 4 flights of stairs & through the door to be seen by Baker.
Warren Commission Exhibit
*The soft drink was not mentioned in the actual report.
Baker immediately turned away & continued up the stairs.