Possible reasons why this man (seen by the Smith family did not come forward:-
...Many, Dad's were carrying their children that night, so he thought that it must have been someone else,
...By the time the news of this man was released, the man seen couldn't remember what day he walked along that road.
...He didn't want to get involved knowing what has happened to others in this case.
...Had reason not to want to get involved....past convictions. visa problems etc
...Died
...He has no resemblance to the photofits ,so is sure it cant have been him
...Was on holiday with a lady, other than his wife
...Afraid of PJ interrogation
Or it could be a combination of some of the above.
Nobody came forward with any evidence and the Laundry man, who did, was too nervous of the PJ, to inform them that he saw a Stranger in the stairwell, so waited to tell Scotland yard........Does that not tell you something?
A lady who was interviewed in her home said that nobody wanted to talk to the PJ and someone she knew, who did talk to PJ, never got another pool cleaning job.