BRATTLEBORO -- In the absence of smoking-gun-style evidence, the murder case against Jodi LaClaire may hinge on which highly trained medical expert jurors choose to believe.

Appropriately enough, the first and only witness to be called to the stand in LaClaire's defense was a London-based expert in hypoglycemia -- the very condition that may have killed LaClaire's alleged victim, 83-year-old Nita Lowery.

And Dr. Vincent Marks wasted no time in contradicting several prosecution experts, arguing that low blood sugar probably did not plunge Lowery into a coma on the morning of March 23, 2009 at Brattleboro's Thompson House care home.

"I am of the opinion that she is unlikely to have had hypoglycemia," Marks testified Thursday in Windham Superior Court Criminal Division.

Marks went even further, saying there is no way to tell what caused Lowery's sudden illness.

"There isn't enough information to make any diagnosis," he said. "I don't know why this poor lady died."

LaClaire, 39, of Bennington, N.H., is accused of giving Lowery what would prove to be a fatal dose of insulin while working as a Thompson House nursing assistant. The elderly woman was found unconscious in her second-floor room and died nine days later, having never awoken from a coma.

LaClaire faces charges including second-degree murder, abuse of a vulnerable adult and seven counts of financial exploitation of a vulnerable adult. Investigators also allege that LaClaire stole Lowery's USAA credit card and withdrew more than $3,000 at ATMs in Brattleboro and Keene, N.H., in the days before Lowery died.

Prosecutors called 28 witnesses over 11 days, resting their case on Wednesday. Defense attorneys Dan Sedon and Richard Ammons promptly moved to dismiss the case based on a lack of evidence; Judge David Suntag, after hearing lengthy oral arguments and reviewing written filings, denied that motion Thursday morning.

The defense called just one witness -- Marks -- before resting on Thursday afternoon.

Sporting thick white hair, glasses and a dark suit, Marks testified animatedly for most of the day. He told jurors he had practiced medicine for four decades while also teaching at the University of Surrey and conducting research.

Hypoglycemia, he said, has been "the dominant feature" of that research.

In fact, Vermont Assistant Attorney General Matthew Levine noted that Marks "literally wrote the book" (simply titled "Hypoglycemia" in 1965) on the topic.

His reputation is such that attorney general's investigators were the first to contact Marks about the Lowery case in 2011.

"I was asked for views informally," Marks recalled. "I gave advice, some of which was followed, some of which unfortunately couldn't be followed because the appropriate specimens were not available."

That was the first of many references to what Marks believes is a critical lack of evidence in the Lowery case. During a short stretch of testimony on Thursday, he offered these observations:

-- "I have to say that the data is appalling."

-- "The evidence is so poor that everything that follows is speculation."

-- "I was amazed at how little genuine hard evidence was available," adding that, "in relation to hypoglycemia, (there is) virtually none."

That likely is why LaClaire defense attorney Dan Sedon, rather than prosecutors, called Marks to the stand. Prosecution witnesses including Vermont's deputy chief medical examiner have concluded that Lowery had low blood sugar, but Marks begs to differ.

"I am skeptical that she was ever hypoglycemic," he said.

He pointed to several factors, including the fact that Lowery did not revive after an emergency dose of glucose. Such a response is a key part of a common diagnostic tool for low blood sugar.

"She showed no indications of improvement," Marks said. "That's not hypoglycemia."

He noted that two initial blood-sugar readings taken by paramedics -- Lowery's sugar was 13 and 16, when normal levels fall between 60 and 100 -- were the result of bedside tests, not laboratory blood analysis.

So-called finger sticks are "not sufficient ... to diagnose hypoglycemia," Marks said.

When there subsequently was a sample of Lowery's blood taken at Brattleboro Memorial Hospital, it showed a "normal figure" of 88, Marks said.

Sedon has asserted that administration of glucose at Thompson House made evaluations of the cause of Lowery's condition much more difficult. On Thursday, during cross-examination, Levine argued that medics had little choice but to give Lowery emergency treatment in an attempt to revive her.

Marks acknowledged that the Rescue Inc. medic who treated Lowery "behaved properly," but he added that "it's created an enormous problem for you as the prosecution."

Sedon has attempted to create other problems for the prosecution by proposing alternative explanations for Lowery's falling ill. Those include alcohol, tumors and malnourishment, all possibilities that Marks expounded on during his testimony.

Marks also said he believes that it takes a "huge" amount of insulin to cause death, adding that hypoglycemic comas can last for hours and not cause irreversible brain damage.

Sedon topped off his questioning of Marks with this: "These are the same opinions you've been giving since the attorney general's office didn't hire you in this case."

However, Marks also acknowledged that his expertise is not all-encompassing.

"It would be impossible for me to write a comprehensive book on hypoglycemia," he said, adding that "it's far too big for any one person."

Levine used that reasoning to point out that Marks' conclusions differed from those jurors already had heard from several witnesses. Those include Dr. Roland Auer, a Montreal-based neuropathologist.

Levine noted that Marks had recommended Auer as an expert witness and asked whether Marks was in a position to contradict a trained neuropathologist.

"I'm only in a position to say that it is an opinion, not a fact," Marks replied.

Auer later was recalled to the stand briefly to rebut Marks' testimony, reiterating that he had observed the "fingerprint" of hypoglycemic damage while examining samples of Lowery's brain under a microscope.

There was no further action from the defense: Following Marks' testimony, Sedon rested his case.

In response to questioning from Suntag, LaClaire quietly affirmed that she had chosen not to testify in her own defense.

That sets the stage for closing arguments today, followed by jury instructions and deliberations.

Mike Faher can be reached at mfaher@reformer.com or 802-254-2311, ext. 275.