Thanks! Pete

Why did the appearance of Frank Pentangelis brother, cause him to change his testimony?
Frankie's brother, Vincenzo's piercing icy stare was knifelike

I believe Frankie was jolted and reminded of omertà by his brother's presence Made him realise, what he was about to do – betray his Don – is a no-no in the business they have chosen and need to honour the omertà