Guilt can be a good thing. It's a soul's call-to-action; the indication that something is wrong. The only way to rid your heart of it is to correct your mistakes and keep going until amends are made. I don't know what you didn't do and what you should've done, but the guilt? The guilt... means your work is not yet finished.
Some people think the Crucifixion only took place on Calvary. They better wise up! Taking Joey Doyle's life to stop him from testifying is a crucifixion. And dropping a sling on Kayo Dugan because he was ready to spill his guts tomorrow, that's a crucifixion. And every time the Mob puts the pressure on a good man, tries to stop him from doing his duty as a citizen, it's a crucifixion. And anybody who sits around and lets it happen, keeps silent about something he knows that happened, shares the guilt of it just as much as the Roman soldier who pierced the flesh of our Lord to see if he was dead.