Jeffrey MacDonald isn't trying to charm today.

Usually, he's unhurried with the visitors who come to see him at the Federal Correctional Institution in Sheridan, Oregon, letting them know by his attention how important they are to him.

How was the flight? he'll ask, blue eyes riveted, perfect teeth set in an appealing grin. The food good? The hotel O.K.?

As likable as a next-door neighbor, he'll go on from there, talking sports, if his callers are fans; literature, if they like books; personal computers, if they're so inclined—though that's a wonder Jeff MacDonald, now in the 18th year of a three-consecutive-life-term sentence, has never seen. He can chat engagingly about anything, from homeopathic healing (a new interest of his) to his Princeton classmates, whose doings he keeps up with in the alumni news. Should mention be made of a relative who's ailing, he can even pass along some well-formed opinions. He was, after all, a very famous doctor in the Green Berets.

Only after he has done all that will the man whose high-school class in Patchogue, Long Island, voted him "most popular" and "most likely to succeed" begin to tell how the government of the United States came to convict him of butchering his pregnant wife, Colette, and their daughters, Kimberly, five, and Kristen, two.

But there are no soothing preliminaries this afternoon. Instead, Inmate 00131-177 is frowning at his watch.

He's bursting to talk, and there's a lot to talk about—starting with an appeals court's recent decision to allow DNA testing on two tiny hairs found beneath the fingernails of his murdered children. Nearly three decades ago, microscopic examination determined they weren't his. If the tests show they didn't come from anyone else in the household, either (and O. J. Simpson's expert Barry Scheck is already drawing up the exam procedures), he has his best shot yet at a new trial...