Hunter Biden, the 49-year-old son of former Vice President Joe Biden, has been dodging discovery requests in connection with a paternity case in Arkansas, and is "the subject of more than one criminal investigation involving fraud, money laundering and a counterfeiting scheme," a private investigation firm claimed this week in a bizarre court filing.

In addition, the Florida-based D&A Investigations told Fox News that its investigators have found that the intelligence community whistleblower at the center of the Democrats' impeachment effort against President Trump accompanied Joe Biden when he traveled to Ukraine in early 2016 and, by his own admission, pressured the country's government to fire its top prosecutor by threatening to withhold $1 billion in U.S. aid.

The whistleblower's attorney, Mark Zaid, did not respond to Fox News' request for comment on D&A's claims, which Fox News has not independently verified. Zaid has previously acknowledged that the whistleblower had "contact" with presidential candidates of both parties, amid reports that he had a "professional working relationship" with one of the Democratic presidential contenders.

On the same day that D&A filed its "Notice of Fraud and Counterfeiting and Production of Evidence," which was first reported by The New York Post and The Daily Mail and obtained by Fox News, Lunden Alexis Roberts -- a woman who claims Hunter Biden got her pregnant -- authored her own motion seeking "primary physical and legal custody" of the child. Roberts also demanded attorneys' fees and a hearing concerning visitation rights.

The court in Independence County, Ark. quickly struck the D&A filing, which was made in a bid to support Roberts' case as an "intervening party." The court said D&A's filing had violated state procedural rules which require that intervening parties raise a claim that shares a "question of law or fact in common" with the existing case.

The firm told Fox News on Tuesday to expect an additional filing soon, and hinted that more incriminating details concerning Hunter Biden's business dealings would soon come to light.

Hunter Biden, in his own motion to strike the firm's claims, told the court the allegations were false and scandalous, and a transparent attempt to garner media attention. D&A, on its website, has openly referred to Democrats' impeachment efforts as a "sham."

READ THE PRIVATE INVESTIGATOR REPORT ON BIDEN'S ALLEGED 'CRIMINAL' INVOLVEMENT

D&A is the same firm that worked with the defense team of Casey Anthony, a Florida woman acquitted of murdering her child in a highly publicized trial in 2011. Anthony later accused the private investigator of smearing her for media attention.

Hunter Biden and Joe Biden pictured in April 2016. (Getty Images)

'COUP HAS STARTED,' WHISTLEBLOWER ATTORNEY SAID IN 2017 POSTS PREDICTING IMPEACHMENT

The firm's incendiary claims highlighted some unanswered questions that could arise in a possible GOP-led impeachment trial in the Senate. Most notably, after leaving the vice presidency, Joe Biden attended a conference at which he discussed a previously unreported meeting in Ukraine for the first time.

"I said, 'I’m telling you, you’re not getting the billion dollars,'" Biden boasted at the conference. "I said, 'You’re not getting the billion. I’m going to be leaving here in --,' I think it was about six hours. I looked at them and said, 'I’m leaving in six hours. If the prosecutor is not fired, you’re not getting the money.' Well, son of a b--ch. He got fired. And they put in place someone who was solid at the time."

The prosecutor, Viktor Shokin, was fired in March 2016, and had widely been accused of corruption himself. However, publicly available records show that Joe Biden did not officially travel to Ukraine in 2016. D&A told Fox News it believes Biden did not take Air Force Two for the trip.

In its filing, D&A investigations asserts that Hunter Biden and his business associates "established bank and financial accounts with Morgan Stanley et al," for the Ukrainian natural gas company Burisma Holdings Limited for a "money laundering scheme," among other ventures.

One alleged scheme "accumulated $156,073,944.24," according to the document.

D&A claimed its filing was necessary because Hunter Biden was failing to answer "reasonable" and "basic" questions in the paternity case, and said it had been "actively investigating" Biden and his partners "since 8 August 2016."

Hunter Biden was a board member of Burisma, which had been under investigation before then-Vice President Joe Biden pressured Ukraine to fire its top prosecutor. In his July 25 call with Ukraine's president that ultimately led to his impeachment, President Trump suggested the Ukrainians look into the circumstances of the prosecutor's termination, including Joe Biden's boast that he had the prosecutor fired.

"Biden went around bragging that he stopped the prosecution, so if you can look into it ... It sounds horrible to me," Trump said on the phone call. State Department officials flagged Hunter Biden's apparent conflict of interest at the time but were shrugged off by the vice president's office.

Joe Biden has denied knowing anything about his son's business dealings. Fox News has obtained a photo showing the former vice president golfing with Hunter and a Burisma executive, and Hunter Biden has previously said he discussed his business dealings on one occasion with his father.

Devon Archer, far left, with former Vice President Joe Biden and his son Hunter, far right, in 2014.

READ LUNDEN ROBERTS' MOTION FOR CUSTODY

Meanwhile, in her filing, the 28-year-old Roberts claims Hunter Biden has "had no involvement in the child's life since the child's birth, never interacted with the child, never parented the child," and "could not identify the child out of a photo lineup."

DNA tests have allegedly confirmed "with scientific certainty" that Hunter Biden is the biological father of Roberts' baby, according to court documents filed in November.

Joe Biden tangled with a Fox News reporter when asked about that development.

“I’m wondering if you have a comment on this report, and court filing, out of Arkansas that your son Hunter just made you a grandfather again,” Fox News’ Peter Doocy asked.

“No, that’s a private matter and I have no comment,” Biden fired back before attacking the reporter.

“Only you would ask that,” Biden said. “You’re a good man. You’re a good man. Classy.”

Hunter Biden is reportedly now expecting a child with his wife Melissa Cohen Biden, whom he married in May.

Earlier this month, Hunter Biden's private life again spilled out into the public sphere when Rep. Matt Gaetz, R-Fla., brought up Biden's admitted past substance abuse issues -- only for a Democratic member to mention Gaetz's own past DUI arrest in response.

Gaetz referenced an article published in July in The New Yorker, which included interviews with Hunter Biden and reported on a 2016 car accident the younger Biden was involved in. According to that story, employees at a rental car agency claimed they found a crack pipe inside the vehicle. It also quoted Hunter Biden describing his attempts to buy crack cocaine in a Los Angeles homeless encampment.

WATCH: GAETZ HAMMERS BIDEN DRUG USE, AND DEM REP RESPONDS IN KIND

“I found this very extensive profile in The New Yorker,” Gaetz said before detailing some of the article’s more sordid details on Biden. “I don’t want to make light of anybody’s substance abuse issues, I know the president is working real hard to solve those throughout the country, but it’s a little hard to believe that Burisma hired Hunter Biden to resolve their international disputes when he could not resolve his own dispute with Hertz rental car over leaving cocaine and a crack pipe in the car.”

Republican lawmakers have questioned why Hunter Biden was being paid upwards of $50,000 a month by Burisma at the same time his father was leading the Obama administration's diplomatic dealings with Kiev. Though the timing raised concerns among anti-corruption advocates, neither the former vice president nor his son has been formally accused of breaking the law.

Fox News' Brian Flood and Andrew O'Reilly contributed to this report.