I read that a red Ford Sierra which JC owned in 1986 - though wasn't the car used to abduct Suzie - was discovered in the year 2000 where it had been sat in a secondhand car sales place for years.
Forensics, according to what I read, found trace evidence of both John Cannan (obviously) and also that of Suzy Lamplugh.
However, the CPS refused to charge JC because:
(A) They wanted a confession
(B) Although the probabilities of both Suzy and JC having been in the car at separate times is probably a million to one or more, it only proved they'd been in the same car. It didn't prove they'd been in the same car at the same time, or that he'd raped/murdered her.
(C) Due to all the huge publicity naming John Cannan as prime suspect, his trial would have been prejudiced.
Regarding the set/sets of keys, it's possible Suzy didn't take them with her, perhaps forgot to as she was apparently showing him two properties - she may have been running late & forgot them. But if Suzy was going on a secret rendezvous under the guise of doing a house viewing (which seems unlikely given her character) she'd still have taken the keys. Why wouldn't she? She'd have created suspicion if she hadn't taken them and someone happened to notice.
And if there were only one set of keys which always remained on the key-board, why didn't her colleagues and manager notice that when she was late back? Her manager phoned Suzy's mum not long after lunch, asking if she'd heard from Suzy. Had the keys been on the board where they should have been kept, he'd have noticed them then, and gone to Shorrolds Road to check inside the house. I believe they did go and check at Shorrolds that afternoon, but I'm not sure if they went inside or not.
Either there were two sets of keys, and the estate agents simply made a mistake and forgot to log that they had two sets (we all make errors sometimes) or there was actually only one set and in Suzy's possible rush to get to Shorrolds Road she realised too late that she'd forgotten them and had to wait for Mr Kipper outside, which was the plan anyway, and planned on telling him they'd have to go back to collect the keys. Remember, they had no mobile phones then, so she'd have had no choice but to wait outside.
Mr Kipper supposedly turned up 15 minutes late and the witness who saw them arguing outside never mentioned seeing them enter or leave the house, and forensics must have poured over it with a fine tooth comb, but there was no trace of either Suzy, Cannan or any other unaccounted for person.