LEBANON, Pa. — Already facing trial in the death of his second wife, retired pastor Arthur Burton ‘‘A.B.’’ Schirmer is now charged with killing his first wife, too, after a grand jury concluded her injuries weren’t consistent with a fall down the stairs, prosecutors announced Friday.

Lebanon County District Attorney David Arnold declined to discuss a motive, but a grand jury report said that Schirmer, 64, had been unfaithful to his first wife, Jewel, throughout their 31-year marriage. Court documents also said the couple had financial difficulties.

Schirmer’s attorney said his client denies involvement in either of his wives’ deaths.

Jewel Schirmer, 50, died at Hershey Medical Center of a traumatic brain injury from a supposed fall. Police and prosecutors reopened the probe after her husband came under investigation in the 2008 death of his second wife, Betty, in the Pocono Mountains. Prosecutors in that case say Schirmer killed his second wife, then staged a car accident to cover it up. He faces trial in January.

Jewel Schirmer’s family, who had long suspected foul play, welcomed the decision to charge the retired pastor.

The district attorney said he did not believe the initial 1999 investigation was botched, though he added that no inquiry is completely free of mistakes.

Schirmer has long said that he was out for a run on April 23, 1999, when he returned home to find his first wife’s body at the bottom of the basement steps. She suffered a fractured skull as well as injuries to her face, body, arms and legs, according to a police affidavit.

But the coroner made no determination at that time as to whether her death was an accident or a homicide.