PHILADELPHIA. For a murder case 44 years in the making, both the prosecution and defense in the trial of accused cop killer William Barnes said Monday that the result boils down to a simple premise: Does the jury agree that two bullets fired into police Officer Walter Barclay in 1966 are

directly to blame for his 2007 death?

If they do, the 74-year-old suspect will spend his remaining days in prison. If not, Barnes’ choice to “maintain my innocence” and pass on a third-degree-murder plea offer of 10-20 years with credit for 16 already served will prove prescient.

Barnes sported a grey suit and eyeglasses in a Courtroom 902 filled to capacity with relatives and visits from Police Commissioner Charles Ramsey and District Attorney Seth Williams.

To open, assistant D.A. Bridget Kirn told the jury of nine women and three men that Barnes shot Barclay after he’d happened upon a break-in attempt on Nov. 27, 1966.

“He should’ve died that night but fortunately, he had an amazing will to live,” said Kirn, noting spastic paralysis led to urinary-tract issues (which were listed on the death certificate), bed sores, ulcers and an eroded quality-of-life. Slated to wed six days later, that ceremony disintegrated.

Called as the first witness, Barclay’s partner that night, Robert Piatek said Barclay was handing out invitations earlier in the shift. “That is the death sentence this defendant imposed. He died day-by-day, moment-by-moment.”

Defense attorney Sam Silver conceded Barnes’ responsibility for the shooting, but said “the evidence will show there is no unbroken chain” linking Barnes to the death, citing multiple motor-vehicle and wheelchair accidents and neglect by caregivers.

Said Barnes brother Jimmy, “No disrespect to Mr. Barclay who had a horrible night, but my brother paid a horrible price already, and now he’s reliving it.”