As his father napped in a bedroom last July, Richard Hanson fired five shots into the 75-year-old man’s face and then fled their Springfield home, prosecutors said Monday as Hanson’s murder trial opened in Fairfax County.

Commonwealth’s Attorney Robert D. McClain did not offer a motive for the killing of Gary P. Hanson, a retired lawyer, but Richard Hanson had argued with his brother earlier in the day and appeared drunk, according to testimony.

Richard Hanson, 53, entered a plea of not guilty to the murder charge and a related firearms charge. Public defender Diego Alcala Laboy described Hanson as a veteran who had a problem with alcohol. Hanson lived in family’s tidy home in the 7600 block of Chancellor Way with his younger brother and mother.

“Richard’s role was as a caregiver. He helped his mom with gardening, babysat kids and took his father on golf outings,” Alcala Laboy said in his opening statement.

Curtis Hanson, Richard’s brother, testified that he and his mother returned home from a dentist’s appointment on July 19, 2011 and found Gary Hanson’s body in a pool of blood on his bed.

During a 911 call played in court, Curtis Hanson identified his brother as the likely killer.

“I cannot believe that son of a [expletive],” he told a dispatcher.

McClain said Richard Hanson used his father’s 45-caliber Glock handgun to shoot him. McClain said Hanson then took his father’s wallet and the family’s green Saturn and drove to Scranton, Pa., where he was arrested at a Red Carpet Inn. Police were able to track Hanson because he used his father’s credit card to make purchases, McClain said.

When Hanson was taken into custody, authorities found his father’s handgun in the trunk of the Saturn, McClain said. Tests linked it to the killing.

Before Curtis Hanson left for the dentist’s appointment, he testified he had gotten into a heated argument with his brother and Richard Hanson had challenged him to a fight. Curtis Hanson said he declined the offer.

It did not appear that there was a financial motive for the killing. Curtis Hanson said his brother did not take valuable gold and jewelry when he left their Springfield home. Hanson also testified his brother was not a beneificiary of his father’s life insurance plan.

Curtis Hanson said his brother did not have a job at the time of the killling.