I believe the so called "roll call" is a combination of the following.
Mr. STERN - Then you got inside the building and what did you do?
Mr. SORRELS - I asked for the manager, and I was directed to Mr. Truly. He was standing there.
I went up and identified myself to him. I said, "I want to get a stenographer, and we would like to have you put down the names and addresses of every employee of the building, in the building."
Mr. STERN - What was your purpose in asking for a list of the employees of the building?
Mr. SORRELS - Because I knew that they would have to be interviewed. I was trying to establish at that time without any delay, who all was in that building or was employed there, because I knew they would have to be talked to later.
In other words, I was looking for someone that saw something.
Mr. STERN - You were looking for potential witnesses?
Mr. SORRELS - Yes, sir.
Sorrels arrived just before 1pm. His actions seem perfectly reasonable.
We also have the report by Senkel that after the shells were found but before the rifle was found (about 1.15pm) Fritz ordered him to take all employees who had been on the 6th floor that day downtown for questioning. So some employees were "in line" on the first floor providing details etc after 1pm and Senkel was determining the 6th floor workers. Presumably he got that information from Truly and or Shelley. Not hard to see that the following individuals would come under attention. Oswald, who had been noticed by Truly in the building after the shooting but was now long gone and Givens, who had been seen by Truly leaving the building well before the shooting.
Others of interest were, Frazier and Norman, who had both been on the 6th floor but was not taken down to City Hall with the flooring crew and Dougherty for reasons unknown as they too fit the criteria for making affidavits as per Fritz's instruction to Senkel. Presumably both were still present in the TSBD at that time or they would have been reported missing too, same as Oswald.