Attorneys for Hunter Biden, in their cross-examination of FBI Special Agent Erika Jensen, attempted to push back on prosecutors' contention that Hunter Biden was abusing drugs at the time he said on a gun-purchase form that he was drug-free.

A key piece of evidence comes from Hunter Biden's 2021 memoir, in which he described his "relapse" just weeks after leaving rehab in August -- just six weeks before purchasing the firearm.

"I stayed clean for two weeks then relapsed," Hunter Biden wrote in his book.

Defense attorney Abbe Lowell, on cross-examination, questioned the assumption that Hunter Biden's relapse implied that he was referring to his drug use -- suggesting instead that he was referring to his alcohol addiction.

"When he was referring to that in his book, was he talking about relapsing to drugs and alcohol, or do you know what he meant?" Lowell asked.

"I can only state what was stated," Jensen said.

"Which is, 'Then I relapsed?'" Lowell asked.

"Just what it says, 'I relapsed,'" Jensen replied.

Jensen also acknowledged that she could not verify that Hunter Biden was continuously using drugs from 2015 to 2019, saying, "My recollection is that there are excerpts where he was principally occupied with smoking crack cocaine. I didn't get the sense that it was the entire history."

"Meaning that there were periods of time that he was not?" Lowell asked.

"I think there -- including the period in August where we have some invoices for rehab, that there were periods where there was not," Jensen said.

It was an important moment for the defense, as Lowell managed to establish that Hunter Biden's use of drugs was not consistent -- cuing up his argument that the president's son was not on drugs at the time of his firearm purchase.

Prosecutors also entered into evidence records related to enormous cash withdrawals Hunter Biden made -- more than $150,000 from September through November of 2018, including a $5,000 withdrawal on the day he purchased the gun. Prosecutors suggested this cash was used to procure drugs; Lowell, on cross-examination, established that Hunter Biden paid $900 in cash for the weapon and accessories.

Court was subsequently recessed for the day, with Lowell's cross-examination of Jensen scheduled to resume Wednesday morning.

Prosecutors suggested that Hallie Biden would be the next witness after Jensen, making it likely that the first Biden family member to testify will take the stand at some point tomorrow.

Testifying for the prosecution, FBI Special Agent Erika Jensen presented evidence involving a 2018 text message exchange between Hunter Biden and Hallie Biden, his brother Beau's widow who was Hunter Biden's romantic partner at the time.

An angry Hunter Biden texted Hallie Biden on the day she discovered his gun.

"Did you take that from me? ... You're being totally irresponsible and unhinged," the text said.

"I just want you to be safe. That was not safe," she replied, referring to his handling of the gun.

Hunter Biden's attorney Abbe Lowell objected to Jensen's testimony regarding the text messages -- which had been obtained by a court-issued subpoena -- arguing that Hallie Biden would be questioned when the government calls her as a witness.

Prosecutors concluded their questioning of Jensen, after which the defense began its cross-examination.

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.

In the first exhibits presented in the government's case, prosecutors played excerpts from the audiobook of Hunter Biden's 2021 memoir "Beautiful Things" -- in which jurors heard in his own words about some of the most personal low points of his yearslong addiction to crack cocaine.

FBI Special Agent Erika Jensen, the government's first witness, introduced about a dozen audio excerpts played out over an hour, as Hunter Biden's voice boomed over the courtroom's loudspeakers while his stepmother, first lady Jill Biden, and several other members of his family sat in attendance.

"I used my superpower of finding crack cocaine anytime, anywhere," Hunter Biden said of the year 2018 -- the same year he purchased the gun that prosecutors say he lied to get. The audio contained passages in which he spoke about the darkest and most dangerous moments of his addiction -- at one point doing cocaine in the bathroom while on a graduation trip with his daughter. .

Jill Biden and her daughter Ashley Biden sat shoulder-to-shoulder as the clips played out, at times leaning their heads against one another. At one point, as Hunter Biden's voice was heard describing a raucous 12-day bender in Los Angeles, Jill Biden lifted her left arm and draped it around Ashley's shoulders.

A person sitting with the family told ABC News they were both "fighting off tears."

Hunter Biden, for the most part, stared intently into the nearby monitor displaying the book's contents, at one point slightly nodding along as he reheard some of his most painful struggles. The jurors appeared largely engaged, with many taking notes and looking up at the screen to follow along.

Taking the stand as a prosecution witness, Hunter Biden's ex-wife Kathleen Buhle described how, after 25 years, their marriage deteriorated under the weight of his drug and alcohol addiction.

Buhle said she first learned of Hunter Biden's crack addiction when she discovered an empty crack pipe in an ash tray on their side porch the day after their anniversary in 2015. Hunter Biden was kicked out of the Navy in 2014 for testing positive for cocaine, and Buhle said ever since then she was "worried, scared" he would abuse drugs again.

When he was on crack, Buhle testified, "He was not himself … angry, short-tempered, acting in ways he wouldn't when he was sober."

She said she would find drug "remnants in little bags" and drug paraphernalia like "a broken crack pipe" -- often enough that she would search his car before allowing her daughters to use it.

In what could be a blow to one of Abbe Lowell's lines of defense, Buhle said Hunter Biden frequently interacted with friends and family, worked, and socialized while under the influence of crack cocaine -- and would often try to hide it from those close to him.

"Did you see him, for lack of a better word, function?" prosecutor Leo Wise asked.

"Yes," Buhle confirmed.