There are numerous pages of questioning about evidence sourcing; too much to post, but here are a couple excerpts.
Interview of Supervisory Intelligence Analyst, Thursday, October 29, 2020, pages 111-112:
Mr. Somers is the majority chief investigative counsel for the Senate Judiciary Committee
Mr. Somers: Do you recall where the information came from that Steele's reporting has been corroborated and used in criminal proceedings?
ANALYST: I drafted that language.
Mr. Somers: And where did you get the impression that his material had been corroborated?
ANALYST: It was based on my understanding that he had been, his reporting had been the predicate for the FIFA investigation.
Mr. Somers: And where did you get that understanding?
ANALYST: My understanding came from the Handling Agent 1 and also SSA-1, who had learned that from Handling Agent 1.
Mr. Somers: And what about the "used in criminal proceedings"?
ANALYST: The same thing. It had predicated the FIFA investigation which actually resulted in indictments.
Mr. Somers: What about "who obtains information from a number of ostensibly well-placed sub-sources"? Where did you get that information?
ANALYST: I'm not sure that I drafted that particular language on there, but it was basically based on the reporting and how things were described within the reporting.
Mr. Somers: Are you aware of the fact that the handling agent said he wouldn't have approved this source characterization statement for Steele?
ANALYST: On the basis of what is written in the IG report, I am aware of that.
Mr. Somers: But you were not aware of it at the time?
ANALYST: Correct.