A good friend used to work for Super Shuttle in Los Angeles. Apparently the Super Shuttle folks spent a lot of time playing dominoes while they waited around to drive people from the Southwest terminal at LAX to strip clubs. This friend, we'll call him "JG", came to visit when we lived in D.C. and he brought his dominoes. There were certain tactical indiscretions that were not permitted. After committing such an indiscretion, JG would tell us "That's the sort of thing that gets you killed in jail." This was what his Super Shuttle coworkers told him, at least.
This case, Commonwealth v. Perkins, SJC No. 07-8448, involves things you shouldn't do when you're in jail.* When folks from the cold case squad want to interview you and they offer you a soda and a cigarette, SAY NO. Because the cold case guys could use the fingerprints on the soda can and the DNA from the cigarette butts to nail you with a murder charge. And there won't be very much you can do about it.
*It's also just a really freaking scary case. If some guy helps you carry your groceries home and then starts showing up at random hours looking to chat with you, do whatever you have to do to make it stop. Call the cops, the Guardian Angels, your brother, your sister, buy a gun (the Supreme Court would wholeheartedly approve!). Just make it stop before something bad happens.