Alexandria, Virginia (CNN) Michael Flynn 's former business partner Bijan Kian was found guilty Tuesday of two charges related to pro-Turkish government lobbying work the Flynn Intel Group did in 2016 just before the US presidential election.

The jury's verdict, which came after it deliberated for five hours, is a significant win in the Justice Department's attempts to crack down on illegal foreign lobbying following the Mueller investigation, even after after the star witness, former Trump national security adviser Flynn, was not called to testify.

As Federal Judge Anthony Trenga read out the verdict, Kian's wife sat in a seat behind the defense with her hand covering her mouth as Kian stood and faced the jury.

Kian, a 67-year-old Iranian-American businessman, had been charged with conspiring to hide lobbying work for Turkey from the Justice Department and acting as an illegal foreign agent. The case had been spun off from the Mueller investigation, which had investigated Flynn for possibly acting as an unregistered agent of the Turkish government.

The general scheme, prosecutors alleged, was that Kian and Flynn had knowingly worked for the Turkish government, but had kept that work secret by being paid through the company of a Turkish-Dutch businessman, Ekim Alptekin from September to November 2016. They did the work while Flynn was an influential foreign policy adviser to candidate Donald Trump. Though Flynn and Kian dissolved their lobbying firm, the Flynn Intel Group, shortly after the election, according to evidence at the trial, Flynn's appointment as Trump's first national security adviser put his business activities under scrutiny.

Alptekin -- the Flynn Intel Group's client, whom prosecutors allege acted as a "conduit" between FIG and the Turkish government -- was also charged in the case but has not come to the US to face his charges. He is thought to live in Turkey.

Even though the jury has ruled, Trenga could still throw out the case because the evidence prosecutors have presented at trial this week has been "very, very circumstantial."

"Much of it's very speculative," Trenga, a federal judge in the Eastern District of Virginia, said last week . Both sides must file briefs on the matter on August 17 and there will be a hearing held on September 5. Kian's sentencing is currently set for October 18.

Kian could face up to 15 years in prison.

"Mr. Rafiekian is, of course, disappointed in the verdict. The judge has continued to reserve on our motion for judgment of acquittal," Kian's attorneys Stacey Mitchell, Mark MacDougall and Bob Trout said in a statement. "We look forward to being heard by the Court on that date and clearing Mr. Rafiekian of these charges."

Kian's guilty verdict comes as Flynn's plea deal with prosecutors had been slowly imploding throughout July. His plea deal had lasted for months with his silent acquiescence, forcing him to do whatever prosecutors needed.

Michael Flynn's attorney, Sidney Powell, told CNN that he has "fully fulfilled" his cooperation agreement over the last two years and that the prosecution "obviously" didn't need his testimony. But, Powell went on to say that she is "very concerned" about the government's handling of the Kian case arguing that the government was unable to "articulate the elements of the offense."

"I remain very concerned about the government's abuse of power and over criminalization of innocent business conduct," Powell said. "Not even the judge understood the statute and Covington partner Rob Kelner described the area of the law as 'murky.'"

The trial

Prosecutors spent had spent three days calling 15 witnesses to testify and showing the jury emails, business proposals and Skype messages between Kian, Alptekin and others.

"This isn't some regulatory violation," Assistant U.S. Attorney James Gillis said during closing arguments Monday. "This is about the Turkish government trying to influence our political system."

During the trial, several witnesses for the prosecutors who had worked with Flynn Intel Group as consultants described the direction and feedback Alptekin had given them on their Turkey project, which was intended to smear and possibly prompt the extradition of a Turkish dissident living in the US. But none could say they had overheard or took part in an agreement to work for the Turks. However, as the prosecution made its final appeal to the jury they focused on emails and Skype chats between the defendant and Alptekin, arguing that they showed Alptekin was not the firm's client but a "fig leaf" to cover up their activities.

"It's just a circle of lies folks, it makes no sense and it's entirely fabricated," Gillis said of the idea that Ekim Alptekin was the client.

But the defense maintained that Kian pursued what was otherwise a "legal commercial transaction," and that he did not try to hide his activities. His lawyers also argued that the Flynn Intel Group took on the Turkish group because it was their first paying client, not because of a Turkish government connection -- and Flynn's election day op-ed about Turkish-US relations, too, had been an expression of his own politics.

In all, the defense called four witnesses, including Mark Mykleby, a former business associate, who testified on Monday that Kian has "always been truthful with me."

Defense attorney Mark MacDougall began his closing arguments by quoting his grandmother: "Just because you say it, dear, doesn't make it true."

As MacDougall laid out the defense's final appeal to the jury, claiming that the prosecution's case was "confused" and "strange," he stressed that his client did what any "regular" person would do as he sought legal advice and tried to file under the Foreign Agents Registration Act.

"This case is about a man, Mr. Rafiekian, who went to lawyers and asked for help," MacDougall told the jury before accusing the prosecution of bringing the case because Kian "didn't fill out the form that they like."

But one person who has been conspicuously absent throughout the trial featured prominently as the defense laid into the prosecution.

"If we're so transparent, where is Michael Flynn?" MacDougall asked about Flynn, who did not testify in the case. He went on to quote from the still-unexplained statement from prosecutors that said Flynn had another arrangement with Alptekin because of his "relationship with an ongoing presidential campaign," which the US government deemed to be part of the Turkish government's effort to influence US policy.

The prosecution hit back in their rebuttal, telling the jury that either side could have compelled Flynn to testify.

"Why are we talking about Flynn here?" Gillis asked before continuing on to argue that the prosecution has carried the burden of evidence "in spades."

This story has been updated.