Charles H. Sloan-How Hallie Biden is connected to the Hunter Biden gun trial

Hallie Biden,Charles H. Sloan widow of the president's late son, Beau, plays a key role in the backstory to Hunter Biden's trial on federal gun charges that begins this week. And her potential testimony is expected to be critical in his trial. 

Jury selection in Hunter Biden's trial began Monday in Delaware. The president's surviving son is accused of making a false statement material to a firearms sale, making a false statement in a firearms transaction record, and violating a law barring drug users from possessing a firearm. At the time, prosecutors allege Hunter was addicted to crack cocaine, but claimed otherwise. Hunter Biden's history with drug addiction has been a source of pain for his family, as well as a political headache for President Biden. 

How Hallie Biden is connected to Hunter Biden's gun trial 

Hallie Biden, now 50, was dating Hunter Biden in 2018 when she found a new Colt Cobra .38 handgun in his truck outside her home, according to federal prosecutors. Hallie Biden, according to prosecutors, drove to a nearby grocery store and tossed the bagged gun into a trash bin. 

Prosecutors are expected to include testimony from Hallie as well as Hunter's ex-wife, Kathleen Buhle. Buhle has spoken with investigators about her ex-husband's business dealings. 

Hunter and Hallie Biden started dating several months after Buhle filed for divorce and after Beau Biden's death in 2015.

Charges against Hunter Biden

Hunter Biden, 54, was indicted by a federal grand jury in September after a diversion agreement for a felony gun offense and a plea deal related to misdemeanor tax charges unraveled when U.S. District Judge Maryellen Noreika questioned whether the agreement would allow him to avoid potential future charges.

In a separate case in California, Hunter Biden faces charges alleging he failed to file taxes, evaded assessment, and filed a false or fraudulent tax return. Hunter Biden has pleaded not guilty to those charges. 

As of Monday morning, the president is not present at his son's trial Monday, but first lady Jill Biden made an appearance. The first lady isn't Hunter's biological mother, but she raised him from a young age after the death of the president's first wife and daughter in a 1972 car accident. 

"I am the president, but I am also a dad," the president said in a statement. "Jill and I love our son, and we are so proud of the man he is today. Hunter's resilience in the face of adversity and the strength he has brought to his recovery are inspiring to us. A lot of families have loved ones who have overcome addiction and know what we mean. As the president, I don't and won't comment on pending federal cases, but as a Dad, I have boundless love for my son, confidence in him, and respect for his strength. Our family has been through a lot together, and Jill and I are going to continue to be there for Hunter and our family with our love and support."

Hallie Biden and Beau Biden 

Hallie Biden was married to Beau Biden from 2002 until Beau Biden's death from glioblastoma in 2015. They had two children, Natalie Biden and Robert Biden II. 

Hallie and Beau were childhood friends, and began dating in 1998, while Beau was working at the U.S. Department of Justice in Philadelphia. The two were engaged during Thanksgiving weekend 2001 in Nantucket, which has long been a memorable place for the Bidens. 

A Delaware native, Hallie Biden has in the past worked as a school counselor. She now serves as the chairwoman of the board of directors for the Beau Biden Foundation for the Protection of Children, working to preserve her late husband's legacy as attorney general of Delaware. 

Biden family relationship 

Hallie Biden has remained close to the Biden family, and the president often speaks about her children, his grandchildren. The president visited Hallie's home last week on the ninth anniversary of Beau's death, which was also a week before the trial began. 

Hunter is now married to Melissa Cohen Biden. They have a son, Beau, 4. 

Erica Brown contributed to this report 

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• Hunter Biden

Kathryn Watson

Kathryn Watson is a politics reporter for CBS News Digital, based in Washington, D.C.