I could be way off the mark here but I think his contract was due to expire at the end of this season. Throughout this season he had been number 1 and Hearts received an offer for him which they accepted. Kello turned this down and as a result was alienated by the club.
/my2cents
I hear you mate, but the SPL is no better than League One. We are letting a Prem class keeper, albeit a bottom 6 one go and a less effective one come in to replace him. IMO, we are not strengthening the squad with this signing.
If thats the case then why have Celtic been European Champions? A long time ago yes but SPL teams still play in the Champions league.
Going by that then, Villa shouldn't have signed Petrov and Carlisle should have instead