I'd read about the "CSI effect," of course -- how the trendy TV show about a crack team of crime scene investigators has juries from coast to coast expecting fancy forensic evidence that will seal a defendant's guilt or innocence. But I was still surprised when it reared its troublesome head in our jury room last week.

I mean, it's one thing to hear the jury foreman in the Robert Blake trial declare that the has-been actor had been found not guilty of shooting and killing his wife because there was "no GSR" (that's gun shot residue, for you non-"CSI" fans) on his hands to nail him beyond a reasonable doubt. The guy was up on a murder charge, after all. But the forensic frenzy materialized in our not exactly earth-shattering firearm and drug possession case here in the District's federal court, too.

"I don't understand why we don't have more evidence," complained one of my fellow jurors. "Why didn't they try to get fingerprints from the car? And off the keys?"

"Why didn't they try to get some DNA, or hair or something, off the jacket?" demanded another.

"Right," chimed in several other voices. "That would make so much difference."

It sure would. It would, above all, eliminate the need to figure out whether the prosecution had proven its case "beyond a reasonable doubt." And that, I have to say, would have been a relief to us all, because if there was one thing my fellow jurors and I wrestled with, it was the question of what constitutes that subjective, shape-shifting notion. What, we pondered and worried, is reasonable doubt?

In this, I guess we weren't so different from the many others who participate in the World of Jury Duty, 2005. By demanding proof positive of a defendant's wrongdoing, lots of jurors these days seem to be reaching well beyond doubt of any kind and grasping for the brass ring of certainty. It seems they aren't looking to get past reasonable doubt; they're looking for no doubt.

The last time I sat on a criminal jury was 1987. That was in the days before "Law and Order" and its many offspring, and way before the "CSI" craze. It was before O.J. and the infamous glove. It was before the much-publicized DNA exonerations of death row inmates in the last several years. Back then, I don't remember my jury having so much doubt about what constituted "proof beyond a reasonable doubt" of the defendant's guilt. A couple of eyewitnesses pretty much did the trick, as I recall. There wasn't any technical evidence at all. No fingerprints, nothing. And we didn't expect any.

But nowadays, there are numerous reports of jurors going wild, researching cases on the Internet and visiting crime scenes in an effort to determine the truth. Aware of advances in science and technology -- and not just from TV shows, as one of our jurors chastised the prosecutor for implying -- they anticipate forensic evidence of the most minute, exotic, even fantastic sort: One member of my jury thought it was possible to lift multiple fingerprints off a given object and determine which set was the freshest. He seemed to hold it against the prosecution -- which has the burden of proof in every case -- for not providing such information. And this was after the prosecutor had gone to great lengths to call a witness who described how hard it is to lift usable prints and explained why the government had no fingerprint evidence of any kind to offer.

These expectations "may be stretching the standard [of reasonable doubt] to perhaps beyond all doubt," says Mickey Sherman, a criminal defense lawyer in Greenwich, Conn. For Sherman -- who unsuccessfully defended Kennedy relative Michael Skakel in his 2002 trial for the murder 30 years ago of Greenwich teenager Martha Moxley -- this is not exactly a negative development. Defense lawyers "prey on it," he said, pushing the idea that every case should include DNA and fingerprints and forensic tests of limitless kinds.

That strategy certainly raises the demons of doubt. But are they reasonable? That's where my fellow jurors and I went round and round. Think how often you hear that phrase -- beyond a reasonable doubt. It's so familiar, a part of the national vocabulary. It's thrown around in novels and movies and on TV. You take it for granted. Until you're on a jury and you suddenly realize you're not quite sure just what it means. And no one will quite tell you. Maybe it's deliberate -- one of those obfuscatory things the legal profession is so fond of, jurisprudence being, in the end, not a science but a flawed endeavor dependent upon human logic and rationality. And emotion, no doubt. But when you're a juror, it certainly is frustrating.

My jury was, if I do say so, a panel of intelligent, eminently reasonable adults. Eight whites, three blacks, one Asian American. Eight women, four men. All professionals of one sort or another, including an accountant, an economist, a paralegal and a couple of us media types. We were well informed, thoughtful, respectful, bent on doing a good job.

But when it came to defining reasonable doubt, a sticking point in our deliberations, we, well, got stuck. "Juries have always struggled with the concept of reasonable doubt," says Robb London, a former federal prosecutor in Seattle and now editor of the Harvard Law Bulletin. (Whew, that's a bit of a relief.)

We all thought we understood that it didn't mean no doubt, or even just a little doubt. But then, how much? And doubt of what? It's taxing, too, to have a guilt-determining standard termed in the negative. When you hear something like what a juror in the Mississippi trial of Edgar Ray Killen said last week -- "I think the reasonable doubt was not there that he didn't have anything to do with it" -- you realize how mind-pretzeling the notion can be.

We deadlocked at 8-4 for acquittal, splintering chiefly over an eyewitness identification of the defendant that some thought too iffy. (Could that police detective really have gotten a good enough look at the guy he chased that night, in the dark, on the run?) Others thought any doubt about the identification question was outweighed by circumstantial evidence that pointed to the defendant as the man who ran from police, dropping a jacket with a gun in the pocket before he headed into the woods. When it became clear no one was going to budge, some in the majority undertook to challenge the minority on their understanding of reasonable doubt.

So we reread the jury instructions the judge had given us. I should know them by heart by now, but I only remember how vague they were. How long and . . . legalistic. The instructions said that reasonable doubt was a higher standard than the one in civil trials, where you only have to believe that the evidence proves the charges are more likely true than not. So all right, not just "probably guilty." But they said proof beyond reasonable doubt doesn't mean scientific or mathematical certainty, either. They said that reasonable doubt is a doubt based on reason. (Go figure.) They said that if after careful, impartial consideration of all the evidence, you were "firmly convinced" of the defendant's guilt, then you should find him or her guilty. But they also said that if you had doubt about any part of the evidence, you had to vote not guilty. I think. And there was more, little of it illuminating.

We requested further clarification from the judge. He instructed us to read the instructions again.

Later, after we had declared ourselves at a stalemate and the judge dismissed us as a hung jury, the attorneys from both sides met with us and offered their own takes on reasonable doubt. It's often stated as doubt based on reason as opposed to fancy, guesswork or conjecture, the prosecutor said. Aha. That's a smidge better, but only a smidge. The defense attorney offered an analogy I can't re-create, but the bottom line was that it means the kind of doubt that would make you hesitate to take a significant action in your own life. Well, okay, but still a little hard to put your finger on.

So I polled a few other lawyers on the meaning of reasonable doubt." It's like pornography," offered defense lawyer Sherman, only half-joking. "You can't describe it, but you know it when you see it." Or, "beyond a reasonable doubt means: My conscience is clear in voting to convict this defendant despite the fact that there are some small, unanswered questions or unknowns, and I'd be shocked and horrified to learn later that he was really innocent," said Harvard's London.

That latter definition has the virtue of being in plain English, though it's pretty broad and nebulous. And again, maybe that's the idea. Who wants a definite, delimited paradigm to follow when you're determining a person's fate? Jurors aren't stamped from cookie cutters; they're individuals who need latitude for their opinions. And yet. . . . During our deliberations, one juror kept pressing the rest of us to quantify our degree of certainty or doubt regarding the defendant's guilt. "How sure are you?" he'd ask. "Fifty-one percent? 75 percent? 99.8 percent?" We mostly shouted him down, dismissing his question as quixotic, if not lamebrained.

But when I talked to former federal prosecutor (now a George Washington University law professor) Paul Butler midweek, guess what? He offered his opinion that the CSI effect was simply reinforcing the very high standard of reasonable doubt, "which most legal scholars put at above 95 percent certainty, probably 97 to 98 percent." Now there's news we could have used! Maybe it wouldn't have changed any votes, but it might have been reassuring to us all to know at least what our certainty level should approach. There's something about a number that can be comforting.

So, as someone who's done her duty, may I offer my two cents to the legal/judicial community? Even if you can't quantify reasonable doubt (the Supreme Court has never done it), could you update the definition a little? Trials are fascinating puzzles, but jurors shouldn't have to rack their brains over obscure concepts that mean so much. Put the instructions in terms the average non-lawyer, non-legal scholar, non-philosopher lay person can understand.

It seems like the reasonable thing to do.

Author's e-mail:

smardzz@washpost.com

Zofia Smardz is an assistant editor of Outlook.

The 'CSI' effect: The popular TV series, featuring forensic detectives whose high-tech methods solve the most difficult cases, have influenced real-life juries, who often look for similar evidence to resolve their doubts, according to prosecutors and defense lawyers.