Hunter Biden's ex-wife has testified about first discovering his drug use, speaking at a criminal trial where prosecutors are trying to prove that US President Joe Biden's son lied about his addiction to illegally buy a gun.
Prosecutors called Kathleen Buhle to bolster their case at the first trial of a US president's child that Hunter Biden knowingly lied about his drug use on screening paperwork when he purchased a revolver in October 2018.
She began her testimony about how she first discovered he was using drugs.
"I found a crack pipe on July 3, 2015," she told the jury, saying it was in an ashtray on the porch of their Washington DC home.
Prosecutors want Buhle's testimony to add to evidence, including text messages, bank records and clips of the audiobook version of Hunter Biden’s memoir Beautiful Things that they say prove he was routinely using crack around the time he bought the gun, including the day after he made the purchase.
Hunter Biden, 54, has pleaded not guilty to three felony charges accusing him of failing to disclose his use of illegal drugs when he bought the gun and of illegally possessing the weapon for 11 days.
Biden has publicly acknowledged his past drug use, including in his memoir, and he told the judge in the case at a 2023 hearing that he had been sober since 2019.
"Addiction is not a crime. Lying is," prosecutor Derek Hines said.
His defence lawyer, Abbe Lowell, has countered that Hunter Biden was not using drugs at the time and did not intend to deceive.
Lowell pressed an FBI agent to acknowledge that prosecutors' evidence of addiction came before or after the gun ownership.
Hines told jurors they would also hear from Hunter Biden's former girlfriend Zoe Kestan, and Hallie Biden, the widow of his late brother Beau Biden.
All three can speak to Hunter Biden’s years-long struggles with drugs and alcohol, Hines said.
On Wednesday, Hunter Biden's lawyer Lowell elicited testimony from an FBI agent acknowledging the bulk of messages about drug use preceded a return to Delaware after a drug treatment stint in California or were sent months after the gun was taken.
Much of Lowell's cross-examination of Erika Jensen, the FBI agent who was called by the prosecution, tried to undercut suggestions that Hunter Biden used $US151,000 ($A227,160) in cash withdrawals around the time of the gun purchase to buy drugs.
Jensen acknowledged she did not know if the money was spent on accommodations, for example.
Hines, a prosecutor, noted that Hunter Biden was using debit cards, not cash, for alcohol and other expenses at the time.
"Do drug dealers accept cards?" Hines asked Jensen.
"Not in my experience," she responded.
As the questioning reached the nearly two hour mark, one juror yawned and spent minutes at a time resting his eyes.
