On the eve of trial, U.S. District Judge Maryellen Noreika threw a wrench in one of the key arguments attorneys for Hunter Biden were planning to advance, ruling that an annotated copy of the federal form Hunter Biden is accused of lying on would be excluded from evidence.

The original document, called an ATF Form 4473, was created in 2018 when Hunter Biden purchased the firearm. But in 2021, gun store employees made a copy that included some handwritten notes. Defense attorney Abbe Lowell contended that employees had "tampered with" the document, and that it raised questions about "who wrote what on the form, and when."

Lowell hoped his argument would undermine the credibility of some key government witnesses -- the people who sold Biden the gun -- and potentially create a reasonable doubt that Hunter Biden was the one who actually checked that box.

Attorneys for special counsel David Weiss' office have said the gun shop employees merely "annotated" the form and urged Noreika to prevent Lowell from introducing it into evidence.

Late Sunday, Noreika sided with Weiss.

Jury selection is scheduled to get underway today in the federal gun trial of Hunter Biden, who authorities say broke the law when he purchased a Colt revolver in 2018.

President Joe Biden's son faces two counts of making false statements while purchasing the firearm and a third count of illegally obtaining it while addicted to drugs.

Although the charges together carry a possible sentence of up to 25 years, legal experts say that, as a first-time and nonviolent offender, Hunter Biden would not likely serve time if convicted.

The trial, in Delaware federal court, is expected to last two to three weeks.

In dramatic testimony, Hunter Biden's former romantic partner Hallie Biden described how, on the morning of Oct. 23, 2018, she went to go "clean out" Hunter Biden's car and found a gun.

"What did you find, in addition to trash and clothes?" prosecutor Leo Wise asked her.

"Remnants of crack cocaine and some paraphernalia," Hallie recounted. "Oh and the gun, obviously."

Hallie Biden said she found the firearm in "the arm console" of the car, which she said was not locked because "the lock had been broken." She said it was the first time she had ever seen a gun. She also found ammunition.

"I panicked, I wanted to get rid of them," she told the jury.

Asked why she panicked, Hallie Biden said she "didn't want him to hurt himself." She said she also worried about her kids finding the gun, saying she considered "hiding" it somewhere but was worried they would find it.

She said those frantic moments led to her throwing the gun in the trash. She told the jury she found a pouch to put it in -- which authorities say later tested positive for having cocaine on it -- and put the gun inside. The jurors were then shown the brown pouch she used.

"I was afraid to kind of touch it, I didn't know if it was loaded," Hallie Biden said, telling jurors she then put the pouch into another bag.

"I took it to the grocery store up the road and I threw it away," she testified.

At this point, jurors were shown surveillance video from the grocery store showing Hallie Biden throwing the gun into the trash.

In the video, her car is seen pulling into the parking lot; she then gets out of the driver's seated, opens the back door to get out the gun, then walks over to the store and places the bag in a garbage receptacle.

"Is that you Mrs. Biden?" prosecutor Leo Wise asked about her image on the video. "Yes," she replied.

Hunter Biden, sitting at the defense table, appeared to be locked on Hallie Biden the entire time, his head resting in his hand. He periodically covered his mouth.