3 year before the murder: You are probably fine, IANAL

10 minutes before the murder: Expect to get an accusation of accessory to murder, conspiracy to murder and a few additional tomes of the penal code. We all know you are innocent, but you should better find a good lawyer just in case instead of wasting your last free minutes arguing on the internet.

When subpoenaed, you'd be obligated to tell the court who you gave the knife to.

But if you'd like to tell the fall, I'm sure some prosecutors wouldn't dig too hard to find the guilty party.