Ben Sheffner's copyrights & campaigns blog reports this, which I think clearly is not a 4.2 problem: blogger sees an interesting set of facts, contacted a witness in the case and blogged about his investigation and what the witness told him. The lawyer in the case has threatened to file a grievance against him for contacting the witness. Ben's great summary and overview is here. The underlying piece that inspired the threat of grievance (warning, it's an awful murder case involving a dead child) is here, on Patterico's Pontifications.
Given that the blogger wasn't representing a client when he made the contact with the witness, I don't see how 4.2 would apply. Also, I don't think the witness was a client of the lawyer, so even if it did, you'd have no violation. I'm not sure how you get an ethics violation.... Anyone? (I know nothing about criminal law.)