Old loyalties? But why would someone loyal to CB (a confirmed really nasty piece of work) place him/herself at the centre of this mess? S/he would automatically be viewed (quite rightly imo) as suspect for that loyalty and be seen as someone ripe for scrutiny?
Regardless of how they might track this person down, bottom line, if they do, this person is going to be minutely scrutinised. So my question remains: what would entice this person to be helpful about the alleged call he and the prime suspect had on the day and in the short hours before the latter is suspected of abducting a child, when they know they would be putting themselves at risk of the type of scrutiny CB is currently under?
Maybe the tip off was told by CB that it was just going to be a petty theft of the apartment?
Once he/she knew it was actually an abduction they could be connected to, they decided they had to keep quiet.OR in the case of it being a woman - perhaps they were threatened with their life if they spoke about it.