With gun store employee Gordon Cleveland on the witness stand, members of the jury saw the Colt Cobra .38 Special that Hunter Biden purchased from Cleveland on Oct. 12, 2018, at StarQuest Shooters in Wilmington, Delaware.

Prosecutor Derek Hines said the encased gun was rendered safe by marshals and asked the judge to allow him to approach with the weapon.

He first brought the gun to the witness stand where Cleveland read aloud the serial number, and then took it to the jury box, where jurors saw the gun that prosecutors argue Hunter Biden obtained illegally by lying on a federal form.

Prosecutors then moved on to question Cleveland about Form 4473, the form that Hunter Biden filled out when he purchased the gun.

Defense attorney Abbe Lowell, cross-examining Hunter Biden's former girlfriend Zoe Kestan, sought to renew his argument that Hunter Biden was not actively using drugs in October 2018 by emphasizing that Kestan wasn't in contact with him at that time and would not know.

Kestan testified that she wasn't in touch with Hunter Biden from Sept. 23, when they were in Malibu together, until November, when he summoned her to Massachusetts while he was trying out a new ketamine therapy program.

As such, Kestan testified she had "no idea" that he had gone back to Delaware, or what he was doing at that time.

"So you didn't see him between those two dates?" Lowell asked.

"No," she said.

Lowell also sought to cast Kestan as an enabler of Hunter's addiction.

"You helped him get drugs?" Lowell asked.

"Yes," Kestan responded.

Prosecutors pushed back on that argument by highlighting their significant age gap: Kestan was 24 at the time of the relationship, while Hunter Biden was 48.

"Twice my age," she testified.

Kestan subsequently concluded her testimony and stepped down from the witness stand. Prosecutors then prepared to called to the stand Gordon Cleveland, the gun shop employee who sold Hunter Biden the firearm in 2018.

Hunter Biden's former girlfriend Zoe Kestan testified that she saw him smoking crack as late as Sept. 20, 2018 -- a timeline that could undercut the defense's argument that he was abusing alcohol and not drugs when he purchased a gun on Oct. 12.

The defense has argued that Hunter Biden was not abusing drugs at the time of the gun purchase, after he had undergone a 12-day rehab stint in California that spanned from late August to early September. They argued repeatedly that when Hunter said in his audiobook that he "relapsed" following that rehab stay, it was only an alcohol relapse.

Kestan, however, testified that in mid-September he used crack "in the bedroom, in the bathroom."

Jurors have been laser-focused on Kestan as she testifies, some sitting up straight in their seats -- in contrast to the earlier testimony from the FBI agent who entered hundreds of text messages and audio book portions into the record, during which some jurors appeared to struggle to remain attentive.

Jurors listened attentively to the testimony of Hunter Biden's ex-girlfriend Zoe Kestan, turning their chairs to face her as she recounted their monthslong relationship in 2017-2018 during his addiction.

Under questioning, she spoke of multiple-night hotel stays, trips to Atlantic City, and memories of night clubs, dinners, and drug dealers.

Evidence displayed by prosecutors during her testimony included highly personal photos she had taken during their relationship, including a photo of her and Hunter Biden in a bathtub together in California, with a crack pipe in his hand.

As Kestan testified, Hunter's current wife Melissa sat in the front row of the gallery, barely moving or reacting.

Sitting at the defense table, Hunter Biden at times rubbed his face or covered his mouth as Kestan recounted their time together and photos flashed across the screen in the courtroom.

"I felt a connection with him," Kestan told the jury.

Prosecutors have introduced Hunter Biden's infamous laptop as evidence while questioning FBI agent Erika Jensen, their first witness.

Prosecutors asked Jensen about email messages found on the laptop and in Hunter Biden's iCloud account that appear to be about his drug use in 2018.

The government had said in pretrial court filings that it was planning to introduce materials on the laptop as evidence in the case.

The laptop has become a symbol of the legal and political controversy surrounding the president's son in recent years. Attorneys for Hunter Biden had previously attempted to preclude the laptop as evidence in the trial, arguing that they have "numerous reasons to believe the data had been altered and compromised before investigators obtained the electronic material."

But special counsel David Weiss argued in court filings that attorneys for Hunter Biden had not "provided any evidence or information that shows that his laptop contains false information," and the judge agreed to admit it as evidence.

Data from the laptop was purportedly obtained and later disseminated in 2019 by a Wilmington, Delaware, computer repairman after the laptop had been dropped off at his shop for repair.

With that context in mind, prosecutors did not rely on the laptop on its own; investigators said they cross-referenced every email, WhatsApp message, iMessage, and text message with Apple Inc. to establish the credibility of the data.

"Ultimately, in examining that laptop, were investigators able to confirm that it was Hunter Biden's laptop?" prosecutor Derek Hines asked Jensen.

"Yes," Jensen said.

"How?" Hines asked.

"Among other things, there was a serial number that's on the back of this laptop that matches the Apple subpoena records that they obtained in 2019, so it matches the registration of this particular device to the iCloud account at a particular date," Jensen said.

"So from the data from the laptop and the hard drive, did you -- what did you do next, or what did the FBI do next when assessing the addiction evidence?" Hines asked.

"So from the data that was extracted from both the iCloud back ups and this -- the laptop, investigators were able to go through largely WhatsApp messages, iMessages, and text messages, and found evidence of addiction within the messages," Jensen said.

Prosecutors also showed jurors an invoice for $85 from the computer repair shop where Hunter Biden dropped off the laptop for repair, which had been sent to an email address belonging to Hunter Biden.

"You said Apple Inc. provided that ... from the iCloud?" Hines asked.

"Yes," Jensen said.