(CNN) -- Previously missing police records on the 1986 shooting death of the brother of Alabama professor Amy Bishop -- accused of gunning down her colleagues last week -- have been found, and investigators said Tuesday they back a state police report that deemed the shooting an accident.





The Braintree, Massachusetts, police records show that police in 1986 believed they had probable cause to arrest Bishop on some charges in her brother's death. However, no charges were filed in that case.





Bishop is charged with capital murder and three counts of attempted murder in a Friday shooting at the University of Alabama in Huntsville, where she was a biology professor. She is eligible for the death penalty in Alabama.





Authorities have said Bishop shot her brother, Seth, at the family's Braintree home in December 1986. A state police report on the 1986 incident was released to the news media over the weekend, but Braintree police said their records of the shooting were missing until Tuesday.





Probable cause existed in 1986 for charges of assault with a dangerous weapon, carrying a dangerous weapon and unlawful possession of ammunition, according to a statement issued Tuesday by the office of Norfolk County, Massachusetts, District Attorney William Keating.





The statute of limitations has passed on those charges, as well as on a potential charge of "wanton and reckless conduct," the lowest standard for manslaughter in Massachusetts, according to the statement.





The recovered documents don't contradict previously released information about the account of the siblings' mother, who told police she witnessed the shooting and said it was accidental, according to the statement.





The statement did not explain how the records came to be missing or when or how they were found.





The December 6, 1986, shooting of Seth Bishop came under renewed scrutiny after Friday's shooting at the University of Alabama in Huntsville.  Authorities said Bishop, also known as Amy Bishop Anderson, was attending a faculty meeting in a university building when she shot six colleagues. She was arrested as she was leaving the building.





On Saturday, Braintree Police Chief Paul Frazier told reporters that the department's records pertaining to the 1986 shooting were missing. Braintree Mayor Joseph Sullivan announced Sunday  a search for the documents had been started, which resulted in the find announced Tuesday.





Describing the 1986 shooting on Saturday, Frazier said that Bishop had fled her home with a gun after she shot her brother and had unsuccessfully attempted to pull over a driver in a vehicle. The newly recovered documents do not refer to an incident involving a vehicle.





Frazier also said that police spotted Bishop and arrested her nearby, but she eventually was released.





"I cannot tell you what the thought process was behind our releasing her at the time," he said Saturday about the decades-old case.





A 1987 state police report released over the weekend cited interviews between police and Bishop's parents, in which her mother said the gun discharged accidentally. Braintree police told state police investigators that "indications were that Amy Bishop had been attempting to manipulate the shotgun and had subsequently brought the gun downstairs in an attempt to gain assistance from her mother in disarming the weapon" when it went off, shooting her brother in the chest.





Read the report on the 1986 shooting





But Frazier said Saturday that Officer Ronald Solimini, who was involved in the case 23 years ago, said that Bishop had shot her brother during an argument.





John Polio, who was Braintree police chief in 1986, also said he recalled reports of an argument between the two.





But neither the 1987 state police report nor the newly found documents detail a disagreement between the siblings.





The state report references a disagreement between Bishop and her father, who was not home when the shooting occurred.





In an uncovered December 6, 1986, record, then-police Lt. James Sullivan wrote that Bishop "stated earlier there had been a family 'spat' and she had gone to her room. (Unknown at this time how much earlier this family 'spat' had been)."





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