In a murder prosecution with no body and no eyewitnesses, the most damning evidence against programmer Hans Reiser is the way he comported himself in the days and weeks following the disappearance of his estranged wife.

Now, after five months of testimony, a jury of 12 will soon have to answer the question of whether Reiser's manner while under police investigation is enough to convict him of murder. They'll have to rule, in effect, on Reiser's "geek defense."

"Jurors are wondering whether he is just odd on the outside," said Richard Waites, a Los Angeles psychologist and attorney. "Or whether he is odd on the outside but with a defective moral structure on the inside."

In his defense, the developer of the ReiserFS filesystem took the stand and displayed himself to jurors as a classic geek: intelligent, paranoid, anti-authoritarian, socially distant and at times logical to the point of irrationality.

Whether this is truly Reiser's nature or not, the archetype is well-known in the computer programming world, and its representatives can be found in groups like the Cypherpunks, Ron Paul supporters, Slashdot users and Wired.com readers. But as Reiser's rambling discourse visibly alienates the trial judge, his own lawyer, and, judging from body language, some of the jurors, the question is whether jurors will understand the geek defense.

And if they do, will they find it adequate to explain Reiser's behavior?

For the geek defense to work, the jury doesn't have to believe that the police investigating Reiser are crooked. Instead, jurors must believe that Reiser believed it himself: that the programmer started with the proposition that police == corrupt and followed it, with irrational logic, right down the rabbit hole.

Reiser testified he believed the police investigating his wife's disappearance would immediately settle on him as a suspect. After consulting several non-fiction books on police murder investigators, he was certain the cops would not be deterred by his innocence. They would even be capable of planting evidence to make a case, he told jurors.

Reiser's demeanor is one of the most important parts of the case. The only forensic evidence is a tiny amount of his wife's blood found on a pillar in his Oakland hills residence, and another speck discovered on a sleeping bag cover in his car, which Reiser says held a bag the two had slept in.

But in the days following Nina Reiser's disappearance on Sept. 3, 2006, Reiser deliberately evaded police surveillance teams, and he traveled 50 miles from his Oakland Hills residence to rent a storage locker in an out-of-the-way town. He removed his car's passenger seat, ditched it and hosed down the interior of the vehicle. And two days after Nina Reiser was last seen, Hans Reiser showed up unexpectedly at their children's school and held a banal but confusing conversation with administrators in which – seemingly like a guilty man – he made no eye contact and could not remember his mobile phone number.

All of that behavior can be explained by Reiser's personality, according to defense attorney William DuBois. But DuBois hoped to keep his client off the stand and establish his personality through other witnesses. He elicited testimony from a psychologist suggesting his client suffered from Asperger's disorder, a mild form of autism with symptoms including socially and emotionally inappropriate behavior, and a lack of appreciation of social cues.

And DuBois called Reiser's parents to the stand to suggest a genetic predisposition to geekiness: His mother, Beverly Palmer, is an artist who was at the Burning Man festival when her daughter-in law-disappeared. His father, Ramon Reiser, is a mathematician who testified in the same rambling style his son would later follow. He even said that it was a family tradition of sorts to discard seats from cars.

Still, Hans Reiser, who enrolled at the University of California when he was only 15, was determined to plead his own case, against his lawyer's advice. When he took the stand in early March, he began fleshing out the defense's theory that his wife, 31, abandoned their children and moved back to Russia, where the couple met.

Reiser told jurors that at the time of his wife's disappearance – as the couple were going through a bitter divorce and custody battle – he had just accused her of bilking his software company, Namesys, out of tens of thousands of dollars. He also claimed that the mother of his two children, a boy now 8 and girl now 6, suffered from Munchausen syndrome by proxy, and made up illnesses for their son. And he testified that his wife, whose last known whereabouts was at his Oakland Hills residence, dated a KGB agent when she lived in Russia.

But Reiser didn't seem concerned that his wife was gone. If he really believes Nina is hiding out in Russia or elsewhere while he stands trial for her murder, his lack of concern is understandable – even logical. But it's the sort of thing that doesn't play well with juries, experts say.

"This guy, while he's on the stand, not showing any compassion, empathy, remorse or general feelings about his wife, he has an uphill battle leading these jurors that he didn't do it," said Marshall Hennington, a Beverly Hills jury consultant.

Reiser's direct examination was also dragged down by his long, rambling answers to his lawyer's questions. That frustrated DuBois, who went so far as to admonish his client to answer "yes or no." Finally, after four days, DuBois abruptly ended his direct examination, almost in mid-sentence: "I have no more questions."

On cross-examination, which began March 18 and is scheduled to continue on April 1, the defendant expounded on the mindset that governed his actions following Nina's disappearance. "I don't trust the government," he told the jury last week. "I don't trust our government."

That's why he removed the two hard drives on his computer before police searched his house and gave them to his attorney, he said. That's why he performed evasive driving maneuvers to determine if police were following him. And that's why he traveled 50 miles to Manteca, California, a tiny town on the way to Yosemite National Forest, to rent a storage locker.

Prosecutor Paul Hora and Hans Reiser spar in court as Hora accuses him of "making things up."

Norman Quebedeau/Wired.com

"You'll admit that one of the reasons you wanted to rent the storage locker was to hide your car?" prosecutor Paul Hora demanded.

"Yes. That was one of the reasons," Reiser replied.

And why Manteca?

"Why not?" the defendant answered.

Similarly, he said there was nothing nefarious about why the floorboard of his Honda CRX was filled with an inch of water when it was discovered by police two weeks after Nina's disappearance. He said the 1988-model vehicle was dirty, so he hosed down the inside, just like he did once with a 1991 Plymouth Laser. But the Plymouth had a hole in the bottom and the water drained out, he said. "I thought they all had holes," he testified.

"Ever heard of shampooing the car?" Hora asked.

"It costs money," the defendant responded. "I'm not sure I even knew at the time you could even rent these shampoo machines."

That missing passenger seat, as it turns out, got tossed into the garbage behind an Oakland hardware store, he said. He testified he removed it for space after sleeping uncomfortably in the vehicle five nights in a row. He no longer wanted to sleep at the Oakland hills house he was sharing with his mother, because, logically, he thought his mother would have had a better chance of winning custody of his children if he wasn't around.

By Thursday, though, his explanations seemed to be wearing thin. The questioning had turned to the day of Sept. 5, 2006, when he showed up at his children's school on the first day of classes after his wife went missing – a day when it was her turn to retrieve them. School administrators had testified earlier that he seemed nervous about something – he couldn't remember his own cell phone number and avoided eye contact.

Why was he acting nervous, prosecutor Hora asked. Did he have something to hide?

"I don't have a specific memory of avoiding eye contact," Hans Reiser testified. "At that time, it was my usual method of interaction to not look people in to the eyes as much as normal people do. Somehow, when I was a teenager, I got the idea that it was kind of impolite to look people in the eyes."

Alameda County Superior Court Judge Larry Goodman chuckles along with jurors as Hans Reiser explains his predisposition not to look people in the eyes.

Norman Quebedeau/Wired.com

The judge chuckled. Some jurors shook their head in disbelief.

Yet Reiser is delivering on his geek defense – not just in his words, but in his manner. It's part and parcel of his claim that he's a little odd, blind to how his words and demeanor affect normal people – non-geeks. Had he offered slick, polished testimony, or openly pined for the woman he'd been battling in family court, observers might like him more. But there might not be grounds to believe him.

"It's risky when a defendant takes the stand, particularly if he isn't clever or if he's too clever," says Edward Bronson, an attorney who consulted on the Unabomber, Timothy McVeigh and Jeffrey Skilling cases. "It's pretty easy for a district attorney to make him look awfully guilty."

To be sure, the jury may have a daunting task deciding whether the defendant's behavior springs from innocent eccentricity or signs of a guilty consciousness, says Howard Varinsky, a trial consultant who has been following the case.

"That's the thing about circumstantial evidence. It has to add up," said Varinsky. "It's the locker room theory. What would your buddies say? 'Give me a break'? Then you can pretty much bet the jury is saying the same thing."