For all of the drama and emotions so far in the Amy Senser hit-and-run trial, its defining moment is likely yet to come.

Not until Senser herself takes the stand Monday will the jurors see and hear what they need to decide this case, according to local attorneys and legal experts.

"It's really going to come down to how she comes across when she testifies," said Hamline University law Prof. Joseph L. Daly. "Does she come across as believable?"

The prosecution wrapped up its case Friday with its hardest piece of evidence casting doubts on Senser's claim that she didn't know she hit someone: testimony from a state expert that Anousone Phanthavong crumpled over her hood when her vehicle struck and killed him.

Senser is expected to take the stand Monday as a defense witness. The case could go to the jury Tuesday morning.

Asked about their take on the case so far, legal observers said it remains her case to lose.

"In my experience criminal vehicular homicide charges are as difficult as any a prosecutor deals with," said Susan Gaertner, a former Ramsey County prosecutor now in private practice. She said it's very difficult to prove such cases without evidence of alcohol use or drug use.

"I think the jurors in these kinds of cases, more than in most criminal cases, have this feeling that 'There but for the grace of God go I,'" she said.

Defense attorney Bruce Rivers said the trial thus far has failed to show that Senser knew she hit someone, which is necessary to convict her of criminal vehicular homicide.

"Where's the driving conduct?" he asked, saying he thinks both sides should have sat down and worked out a plea deal rather than go to trial. Senser faces three criminal vehicular homicide charges: one for leaving the scene and the second for failing to immediately call for help. The third charge of operating her vehicle in a grossly negligent manner was added 10 days before the trial started.

Rivers said that the last charge requires proof that Senser was driving in a way that would "shock the conscience."

"Seeing the bit of testimony that I have, knowing what a sideshow it is, I see the defense as winning this case," he said, adding that he would never underestimate prosecutor Deborah Russell.

The story that the defense has told thus far -- that she didn't stop because she thought she hit a construction barrel or traffic cone -- didn't impress William Mitchell law Prof. Ted Sampsell-Jones as believable. Still, the burden is on the prosecution to show that she knew she hit a person, he said.

"You can't see inside people's brains. You have to look at their external behavior, and the jury has to make a common-sense judgment at some level," he said.

Senser, 45, of Edina, came forward as the driver 10 days after she struck and killed Phanthavong, 38, a chef from Roseville, as he was putting gas in his stalled car on the Riverside Avenue exit ramp on Interstate 94 in Minneapolis.

Talk of affair debated

Longtime Twin Cities criminal defense attorney Joe Friedberg said it "boggles the mind" that the trial included talk of an extramarital affair. That happened Thursday, when Russell followed up on Joe Senser's testimony the day before that his wife had not lied to him in their 22 years of marriage. "Not about having affairs with other men?" she asked. After he replied that he never asked her about affairs, she asked if he had ever caught her in inappropriate relationships with other men. He answered no.

Friedberg said Joe Senser's testimony that his wife never lied to him opened the door for Russell to ask him about his wife's character, including questions about an alleged affair.

"The last thing in the world you want to come out is the possibility that this lady who everybody thinks is a pretty nice lady has had an affair either known or unknown to the husband," he said.

Former prosecutor and current criminal defense lawyer Tom Heffelfinger agreed.

"I seriously question what relevance the fact that there may be discord within the Senser family has to do with whether or not this woman is guilty of three counts of vehicular homicide," he said.

In September, Senser's defense attorney, Eric Nelson, told the Star Tribune that Senser will base her defense on a recent Minnesota Supreme Court reversal of a man's conviction in a similar case where the state failed to prove that he knew he struck and killed a man changing a tire when he left the scene. The Supreme Court's 2010 decision in the case of Mohammed Al-Naseer effectively means that prosecutors must now prove criminal intent by drivers who leave the scene of accidents, said Nelson.

'Truly a tragedy'

Heffelfinger also questioned what he called the "shotgun approach" to the charges against Senser. "It seems to be that the charges against her are analogous to throwing mud against the wall and seeing if something will stick," he said.

"It's truly a tragedy," he said. "A young man lost his life and this woman's life and her family's life will never be the same, but that doesn't mean that the government, the state, has a good case."

Defense attorney Earl Gray said he was equally surprised by the talk of an affair, but thought it would backfire on the prosecution. "What couple has not had some problems and what does that have to do with whether or not she knew she had hit somebody?" he asked.

Friedberg said as much as he's puzzled by the case, it's hard not to follow it.

"It really seems like a dime novel," he said. "It's kind of turned into a soap opera, hasn't it?"

Matt McKinney • 612-217-1747