HARBESON, Del. — A paraplegic man who was shot and killed by Delaware troopers executing a search warrant at his home had a long criminal history that included convictions for drug trafficking, robbery and resisting arrest, court records show.

Delaware State Police said Wednesday that Robert Knox, 50, of Harbeson was lying in bed and reached for a handgun while troopers were in the home early Tuesday. A struggle over the weapon followed and two troopers fired their weapons at Knox, who later died at a hospital.

The incident is being investigated by the state police homicide unit.

Knox's father, Andrew A. Knox, 82, was arrested Tuesday and charged with possession of a firearm by a person prohibited and maintaining a drug property. He was released on $13,000 unsecured bail. A defense attorney who is expected to represent Knox said Wednesday that he was waiting to hear back from the family.

State police said Wednesday that Knox's arrest followed a three-week long drug investigation in southern Delaware that also resulted in the arrest of Andrew Ayers, 54. Ayers, who was arrested at a house in Milton, was being held on $100,200 secured bond.

Police said they recovered four handguns at the Knox residence, along with about 1.8 pounds (815.8 grams) of powder cocaine, 2.6 pounds (1,196.9 grams) of marijuana, 2.4 ounces (68.2 grams) of crystal methamphetamine, and 1.8 ounces (51.9 grams) of crack cocaine.

At the house in Milton, officer seized about 14 ounces (395.6 grams) of marijuana, along with crack cocaine and a loaded handgun. Ayers is facing drug delivery and gun charges. It was not immediately clear whether he has lawyer.

The elder Knox has previous convictions for possession with intent to sell drugs, possession of a firearm by a person prohibited, burglary, theft and conspiracy.

Robert Knox was convicted of drug possession in 2015. He was convicted in 2003 of trafficking cocaine, possession with intent to deliver, delivery of a narcotic, reckless endangering and resisting arrest. He was also convicted of cocaine trafficking and conspiracy in 1994, and on robbery charges in 1988 and 1989.

According to a newspaper article at the time, Knox and his father were arrested in February 2003 after police found drugs and guns in the father's home. According to the article, Robert Knox tried to flee the scene in a car, driving toward police officers, two of whom shot at the car in self-defense.

Juanita Knox, Andrew's estranged wife, said she had spoken to him Tuesday, but she did not provide any other details.

"I really don't know the ins and outs of it yet," she said when asked about the shooting.

Knox said her son was paralyzed from the chest down in a car accident in 2013.