He suffered for a long time after it because of the presumption of guilt; conceivably, that may partly have been due to the nature of trust for the police at the time.
To be fair, I can't say he didn't do it, however based purely on the evidence provided I doubt there'd be much chance that he'd have ever face trial today.
Purely talking speculatively, you could suggest he had an accomplaice when you consider specifically asking for the time and his 'numerous' interactions.
However, on the other hand I'd never seen the taxi to Sefton Park article before (it's in the original Wallace thread) and that instantly made me thing.
If I remember correctly, the tram along Menlove Avenue would have gone from Penny Lane, which isn't too far from Penny Lane if you stop near Greenbank.