First son Hunter Biden was convicted last week on a trio of federal gun charges that stemmed from his lying about his otherwise admitted illicit drug use to illegally purchase a handgun in 2018 -- a conviction that his lawyers plan to appeal and hope to overturn.

On Monday, Biden's attorneys filed a motion calling for a new trial but then inexplicably withdrew the filing from the docket, according to the New York Post.

The motion sought to have the recently concluded week-long trial and resulting conviction vacated on a jurisdictional technicality, and it is unclear why the legitimate if obscure legal argument was so swiftly rescinded after it was filed.

A technical argument on jurisdiction

At issue here in the since-retracted Monday filing, according to CNN, is what is known as the "mandate" by which a higher appellate court returns jurisdiction to a lower trial court, given that lower court proceedings in a case are typically paused while appeals are pending.

Biden's attorneys had filed two pre-trial appeals with the 3rd Circuit Court, both of which were denied by three-judge panels, as was a request for a rehearing by the entire appellate court on one of those appeals, after which the district court in Delaware proceeded with the trial that ended with a guilty verdict on all three counts.

The defense attorneys argued, however, that the 3rd Circuit had never issued its "mandate" to return jurisdiction to the lower court to authorize further proceedings, which should render the entire ensuing trial and conviction null and void.

"Biden’s convictions should be vacated"

In the nine-page motion for a new trial, Biden's attorneys noted that two pre-trial appeals had been filed on April 17 and May 20, both of which had the effect of pausing all proceedings in the district court of Judge Maryellen Norieka.

"The Third Circuit entered an order dismissing the first appeal on May 9, 2024, but the issuance of the mandate was delayed while the Third Circuit considered Mr. Biden’s petition for rehearing and rehearing en banc," the motion acknowledged. "The Third Circuit entered an order dismissing Mr. Biden’s second appeal on May 28, 2024, and denied Mr. Biden’s rehearing petition on the first appeal on May 31, 2024."

"The Third Circuit, however, did not then and has not yet issued its mandate as to the orders dismissing either appeal," the attorneys continued. "Thus, when this Court empaneled the jury on June 3, 2024, and proceeded to trial, it was without jurisdiction to do so."

The motion pointed to several precedent cases, predominately from the 3rd Circuit, that outlined how jurisdiction is removed from a district court by a pending appeal until returned via the appellate court's mandate, and stated, "Naturally, any district court action taken after it has been divested of jurisdiction by an appeal must be vacated."

That general rule applies even if the circuit court ultimately rejects the appeals and returns jurisdiction to the district court at a later date after a trial has commenced, Biden's attorneys argued. "Accordingly, the law is settled in this Circuit and dictates that the Court must vacate Mr. Biden’s convictions and order a new trial."

In the end, the defense attorneys asserted, "Mr. Biden’s convictions should be vacated because the Court lacked jurisdiction to proceed to trial."

No comment on withdrawn filing

The motion from Hunter Biden's attorneys was filed Monday morning but just as quickly withdrawn, and the district court's docket now reads: "The Motion for a New Trial (formerly DI 233) has been deleted at the request of counsel."

CNN asked Biden's attorneys for an explanation of why the filing was retracted but they did not respond to the request for comment.