Hallie Biden, a former girlfriend of Hunter Biden and widow of his brother, Beau, took the stand on Thursday, telling jurors that she saw him buy, stash and smoke vast amounts of crack cocaine in the fall of 2018 when he claimed to be drug-free on a firearms application.

Hallie Biden — speaking in nervous, clipped bursts as she faced Biden across the fourth-floor courtroom — admitted that he had introduced her to crack in the summer of 2018. She said she was ashamed and embarrassed by their behaviour when the two briefly lived together in a rented house in Annapolis, Maryland, at a time when both were in shock over Beau Biden’s death.

“It was a terrible experience that I went through,” she said.

Hallie Biden is, by far, the most important witness for the prosecution, offering the most detailed, and intimate, portrait of Hunter Biden’s reckless and self-destructive behaviour at the time.

Hunter Biden, she said, bought multiple rocks of crack in Washington, where he kept an apartment — some the size of “Ping-Pong balls, or bigger maybe” — and stored them in his “backpack or car”.

Hallie Biden said she discovered the gun at the centre of the case when she was rifling through Hunter Biden’s vehicle the morning after he showed up at her house. It was part of a “pattern” of erratic behaviour, she added, saying he would be unreachable for weeks at a time and she or her children would scrounge through his car for drugs or alcohol to help him “start anew and deal with stuff” .

When she searched the car on October 23, she described noticing “a dusting of powder” that she assumed to be “remnants of crack cocaine” before finding the gun in a case with a broken lock. Flustered, she said she improvised a way to dispose of it at a grocery store nearby. Prosecutors then showed surveillance video of her tossing the gun only to return later and frantically try to recover it.