Does he clearly say that none of them attended the vigil? I must admit that I can't totally understand what this discussion is all about. I just remembered that Knox herself had stated that they were there, attending the vigil. That there are different media stating different things happens all the time unfortunately.Why not use John Kercher's book when making claims about what they did in Perugia? He says quite clearly what they did and when.
They arrived on the 5th and left on the 6th. Her father left the note on the 6th (according to the link below) but that does not mean that they did not attend on the 5th. Or maybe her father did not attend and the other family members did, or whatever you want to make of it. I have no idea why it must be denied that they did not attend her memorial. They have her memorial every day.
http://metro.co.uk/2007/11/07/meredith-flatmate-heard-screaming-471270/