Nope. They could use a warrant to compel the sender or the recipient of the messages to unlock them or face jail time. But Apple doesn't have the keys.
I think the most important thing here is that law enforcement must approach the individual. What happens next may end up a complicate web of legal acrobatics, but the individual at least knows the law is after them. That's a good thing, IMHO. If your privacy is being violated by police forcing you to open your phone to them... at least you know the "when", "how" and "what" info they're getting. I'm also pretty sure you'd at least have a strong suspicion on the "why" it's happening to you as well - fair or otherwise.
