So his defence is that he was a really, really bad newspaper editor?
I’ve only edited a small regional weekly with a readership in the thousands but during that time I had to know everything my reporters were doing because IT WAS MY JOB. Not all of my job, to be sure, but a significant part of it. If a reporter had filed a story and I didn’t know the source, I would have checked because, for example, somebody might mount a legal challenge such as, I don’t know, the one Coulson is facing now.
Ignorance is no excuse. If that really is his defence, I’ll be amazed if anyone gives it any credence at all.