Jurors in the felony gun trial of Hunter Biden on Tuesday heard the same words that prosecutors used last week to justify the prosecution of former US president Donald Trump, who was convicted of 34 felonies in New York City: "Nobody is above the law."

Then prosecutor Derek Hines told the jurors in his opening argument at a Wilmington, Delaware, courthouse: "Nobody is allowed to lie, not even Hunter Biden. It doesn't matter who you are or what your name is."

President Joe Biden's son has been charged with three felonies stemming from the purchase of a revolver in 2018 when he was, according to his memoir, addicted to crack cocaine. He has been accused of lying to a federally licensed gun dealer, making a false claim on the application by saying he wasn't a drug user and illegally having the gun for 11 days.

The prosecution and defense disagreed about when he was using illegal drugs and whether the timeline affects the gun charges against him.

Hines said his drug abuse occurred before, during and after buying the gun in October 2018. He spent hours Tuesday on Biden's drug problem, using his own words and memoir to show the depth of the addiction.

He had FBI agent Erika Jensen, who has investigated the case, go through passages from Biden's memoir where he discusses his addiction and times that he had smoked crack.

Hines said that the salesman who helped with the purchase would testify that he saw Biden check a box on the federal form indicating he wasn't using drugs.

"He crossed the line when he chose to buy a gun and lied about a federal background check," Hines said. "We would not be here today if he was just a drug addict. The defendant's choice to buy a gun is why we're here."

Defense attorney Abbe Lowell, one of Hunter Biden's lawyers, opened his argument by emphasizing the word "knowingly".

He suggested that prosecutors left out the word from the slide that described the charges to the jury.

Lowell said he would disprove the government's core contention that Biden "knowingly" broke the law by answering "no" on a question asking applicants whether they were using drugs at the time they sought to purchase a gun.

Biden "knowingly violated the law" is what prosecutors have to prove, Lowell said. He stressed that it is about what Biden thought at the time in 2018 and what his state of mind was when he walked into the gun store.

He told jurors that prosecutors can't prove at the time Biden bought the gun that he believed himself to be addicted or an unlawful user of drugs.

Lowell said the form Biden signed asks whether you "are" a drug user. "It does not say ‘have you ever been,'" and he suggested Biden didn't think of himself as someone with a drug problem when he purchased the gun.

Lowell argued that Biden was abusing alcohol and not drugs when he purchased the gun and when he said he was not a user, his understanding was that he was not at that point.

Lowell said that Biden had been in rehabilitation in California months before buying the gun and wasn't using drugs at the time of the gun purchase or in the preceding weeks.

He said much of the Justice Department's evidence of Biden's drug use comes from other periods of his life and has little relevance to the time period at issue in the indictment.

Biden, 54, is the first child of a president facing criminal charges.

For a second day first lady Jill Biden and other members of the president's family looked on from the front row. She left after lunch to be in Washington.

Both the gun charges and the tax charges were to have been resolved through a deal with prosecutors last July.

But US District Judge Maryellen Noreika, who was nominated to the bench by Trump and is overseeing Biden's trial, questioned aspects of the deal.

The lawyers couldn't agree to a resolution on her questions, and the deal fell apart. Attorney General Merrick Garland then appointed a former US attorney for Delaware, David Weiss, as a special counsel in August, and a month later Biden was indicted.

Agencies contributed to this story.