My humble opinion is that this is a combination of boeings' incomplete AMM and the crews inability to realise what the problem was when the cabin altitude warning sounded. Nevertheless responsibility lies with the management of Helios who although received 5 reports from F/O's about the certain Captain, continued to employ him. Apparently the reports dissapeared by magic although the F/O's involved gave the info to the police during their testimony.
Finally as a proffessional pilot myself and as some of you have commented, i take it as my responsibility to prepare my a/c prior a flight and make sure all is ok. We must learn as pilots to learn from ours and other peoples mistakes and take responsibility for them.
As for the inquiry i hope justice is awarded.
Fly safe.