He was interviewed nine times in all, at least three times directly because of the fiver line of enquiry - twice in November 1977 and once in January 1980. See here:
http://www.execulink.com/~kbrannen/intervws.htm
When you put it like that, though, I'll concede that I'm being too harsh in saying that they "should" have caught him. In the initial two interviews, he was only one man out of about 8.000 they had to cover and he was given an alibi by his wife for the night when the killer had returned to Jordan's body. You can't blame them for moving on. By the time of the next interview about the fiver, in January 1980, they knew he was one of 241 men who could have received that banknote. Thinking about it, it was probably an exceptional piece of work to be able to narrow it down like that. My criticism at that stage isn't of the Manchester detectives who did the work to identify who could have got the note. It's that the West Yporkshire detectives then decided not to pursue as a suspect a man who was one of the 241 and who should have set off alarm bells for various other reasons. This decision was due in some significant measure to him lacking a Wearside accent. My criticism really is that they made a disastrous error in keeping their faith in the authenticity of the tape when, by this stage, it should have been obvious that it was a wild goose chase.
As you say, the tyre track enquiry would eventually have led to Sutcliffe, though that was also wound down for reasons of manpower. The car sightings in red light areas was also incriminating - he was one of a very small number of punbters whose car was seen in the operations in all of Leeds, Bradford and Manchester. Unfortunately, they were swamped by the volume of information that came in. Information about Sutcliffe was kept on four separate index cards because often, something would come to light about him and the other cards would still be stuck in the backlog, waiting to be reviewed by senior detectives. If they could have seen all the information about him in one place - as they could now with a computerised system - they'd have understood much earlier that this was a guy they should be looking at very closely. As it was, I believe at some point they compiled a list of the top 50 suspects - and Sutcliffe wasn't on it!
Yes, I've seen an interview with Bruce when he talks about finding the body. Must have been a terrible experience.
The hoaxer, in a letter before the Vera Millward murder, also promised that his next victim would be an "old slut" in Manchester or Liverpool. I think that also made them think there was a decent chance the tape, when it came, was genuine.