My guess is the latter. He went up to the sixth to investigate. Then came down to the first.
My personal view is that Dougherty was not on the 5th floor just before the shooting.
Norman and Jarman walk from the north-west corner of the 5th to the south-east corner and do not see Dougherty.
Wiliams walks from the north-west corner to the south-east corner and does not see Dougherty.
All three men run from the east side of the building to the west and do not see Dougherty.
Dougherty must be on the 6th before Norman and Jarman arrive.
Dougherty must be on the 6th while Williams is still up there.
For me, Dougherty is the number one candidate for Rowalnd's man with a rifle on the 6th floor around 12:15