A federal jury last week acquitted the final two men on trial in an unusual online drug conspiracy case involving the cooperation of its elusive ringleader — but not his testimony.

Jurors in St. Paul found physicians Elias Karkalas and Prabhakara Tumpati not guilty on all counts late Friday after beginning deliberation Thursday afternoon. Days earlier, U.S. District Judge Susan Richard Nelson acquitted two other co-defendants after finding that prosecutors had presented "simply a dearth of evidence" to support charges including conspiracy to violate federal laws regulating prescription drugs and conspiring to commit international money laundering.

"It was much more about [how] the government didn't prove their case than anything any of us did," said Paul Schneck, an attorney for Tumpati.

Prosecutors from the Justice Department's consumer protection division spent more than two weeks presenting their case, drawing on business records and wiretap evidence to bolster claims that the defendants helped RX Limited amass more than $200 million in questionable prescription pill orders. They said Karkalas and Tumpati authorized online sales of prescription drugs without physical examinations or valid doctor-patient relationships and earned more than $2.3 million and $1.1 million, respectively.

The case stemmed from a U.S. Drug Enforcement Administration investigation initiated in Minneapolis in 2007. It led to the 2012 arrest in Liberia of Paul Le Roux, who has since been linked to gun running, computer hacking and — according to his own testimony — eight international murders. Le Roux cooperated with authorities soon after his arrest and is being held under witness protection as he awaits sentencing in a separate case charged out of New York.

Prosecutors did not call Le Roux to testify against his former employees, but attorneys for Moran Oz and Lachlan McConnell — whom Nelson acquitted March 6 — had planned to question him while mounting "duress" defenses that their clients worked for the RX Limited boss under fear for their lives.

"I believe the jury reached the same conclusion that all of us eventually reached after working on this case for three years," said Joe Friedberg, an attorney for Oz, who was acquitted by Nelson. "That was that the entire prosecution was immoral. You don't take the big guy and, especially when he's a horrible person, accept what he tells you at face value. And then attempt trying the case without calling him as a witness."

In a written statement Monday, Nicole Navas, a Justice Department spokeswoman, said the government was disappointed in the outcome but respects the jury's verdict.

"However, this decision will not impact the Justice Department's ongoing commitment to holding individuals accountable who violate the federal Food, Drug, and Cosmetic Act and put consumers at risk," Navas said.

Daniel Gerdts, one of two attorneys for Karkalas, called the three years between his client's arrest and acquittal "a real tragedy."

"It ruined his personal life, ended his medical practice for at least the past three years and was completely unnecessary," Gerdts said.

Stephen Montemayor • 612-673-1755

Twitter: @smontemayor