(CNN) -- A biology professor charged with killing three faculty members at the University of Alabama in Huntsville fatally shot her brother more than 23 years ago, but she and her mother claimed the shooting was accidental, according to documents released Sunday.

Amy Bishop Anderson was 19 when she fatally shot her brother, Seth, on December 6, 1986, in Braintree, Massachusetts, according to a Massachusetts State Police report released Sunday. She was never charged in that shooting.

Anderson was charged this weekend with capital murder in Friday's on-campus shooting deaths of her colleagues. She could face the death penalty.

The state police report in the 1986 shooting, released by the office of U.S. Rep. Bill Delahunt, D-Massachusetts, gives an account similar to a Boston Globe story published on December 8, 2008. Delahunt was district attorney at the time; staffers said he was in the Middle East on Sunday and unable to comment on the case.

Earlier this weekend, Braintree police said records from that shooting were missing, and that the department's log indicated the shooting was accidental. However, Police Chief Paul Frazier said he didn't agree with the Globe's account.

The Globe's story stated that Anderson asked her mother how to unload a round from a 12-gauge shotgun and that Anderson -- then known as Amy Bishop -- accidentally shot her brother while she was handling the weapon. The article cited then-Police Chief John Polio as the source.

According to the state police report released Sunday, Braintree police told state police 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, Seth, in the chest.

But, Frazier said Saturday, "it is a far different story I believe than what was reported back then. I cannot tell you what the thought process was behind our releasing her at the time."

An officer then involved in the case who is still working for the department told him that Anderson shot her brother during an argument, Frazier said.

The officer said Anderson allegedly fired a shot in her bedroom without hitting anyone, argued with her brother, shot him and then fired another round in the home before fleeing, according to Frazier.

Frazier said the teen was arrested after pointing a weapon at a vehicle near the house in an attempt to get the driver to stop, but it drove on. But during the booking process, then-Chief Polio called and told the officers to release her, Frazier said. He said her mother was at the time a member of the Braintree Personnel Board.

In a telephone call with CNN, Polio, now 87 and retired, denied ever calling in the order. He said detectives including lead investigator Capt. Theodore Buker -- who has since died -- had interviewed Anderson and her mother, Judith, who is identified in the state police report as J. Bishop.

Buker told him that the shooting appeared accidental and the two men agreed she should be released to her mother, Polio said. A request was then filed with Delahunt's office to conduct an inquiry, but Delahunt never did so, he said.

The state police report, however, said that Buker met with a state police investigator and determined that "due to the testimony of the members of the Bishop family, and in particular the testimony of J. Bishop, relevant to the facts concerning the death of Seth Bishop that no further investigation ... was warranted," the report concludes. Seth Bishop's death was listed as accidental and the investigation was concluded.

Delahunt spokesman Mark Forest told CNN the state police and medical examiner concluded the death was accidental, and an autopsy was also conducted. "The investigative reports ... did not recommend any further action," he said in an e-mail. Those reports were turned over to state and local authorities, including the district attorney's office, he said.

Anderson's mother witnessed the shooting, the state police report said. Investigators waited 11 days to interview Anderson and her parents because of their "highly emotional state" following the shooting, according to the report.

In the December 17, 1986, interview, Anderson told authorities she "thought it would be a good idea if she learned how to load the shotgun in the house," according to the state police report. The young woman told police she was concerned for her own safety after the family home was broken into, although she previously had been afraid of the gun.

She said she got the gun and loaded shells into it, but was unable to get them out. Anderson said that while she was attempting to unload the weapon on her bed, it went off. She then took it downstairs to ask for help in unloading it. She asked her brother, she said, and he told her to point the gun up instead of carrying it beside her leg. Her brother was walking across the kitchen between her and her mother, she said. She started to raise the gun, and "someone said something to her," she recalled in the report. She turned and the gun went off.

"Amy thought that she had ruined the kitchen but was not aware of the fact that she had struck her brother," the report said. She fled, and told police she thought she had dropped the gun as she ran away. "She cannot recall anything else until she subsequently saw her mother at the police station," the report said. The report does not reference any other shots fired besides the one in Anderson's bedroom and the shot that struck her brother.

Anderson's father was not home at the time. He told police he had had a disagreement with his daughter "about a comment she had made" before he left to go shopping. He told police he had bought the shotgun about a year before the shooting, after the house had been broken into, and that he and his son belonged to a rifle club. Anderson was not trained to use the gun, he said.

Anderson's mother said that when her daughter came downstairs and asked for help in unloading the gun, she told her not to point it at anyone, and that her daughter turned and the gun went off. The woman told police she did not hear the shotgun fire earlier in her daughter's bedroom and "believed the house was relatively well soundproofed and that such a discharge would not necessarily be heard on another floor of the house."

Polio acknowledged that an argument had occurred during the shooting and said that the other shots, including one fired into the ceiling, did not appear aimed at anyone. He also recalled that Anderson had fled the scene. But, he said, he could not remember what he had told the newspaper in reference to the case or why details, including the argument, were not reported.

He said Anderson's mother had worked for the personnel board and at one point was assigned to the police department. But he rejected as "laughable" any suggestions that the suspect's mother might have influenced their handling of the case.

"There was no cover-up," Polio said. "Absolutely no cover-up and no missing records. The records were all there when I left. Where they went in the last 22 years and two police chiefs subsequent, I don't know."

Braintree Mayor Joseph Sullivan announced Sunday an effort to locate all materials associated with the shooting.

"The Braintree Police Department will conduct a thorough audit of all its records to identify if there were deficits in its past recordkeeping process," Sullivan said. "It is important to note that in 1986, police records were created and maintained manually, which complicates their review and retrieval."

The Braintree shooting resurfaced after Harvard-trained Anderson was charged in Friday's shooting in Alabama. Huntsville Police Chief Henry Reyes said Saturday that Anderson was attending a faculty meeting on the third floor of the sciences building Friday afternoon when she brandished a gun and shot six colleagues, killing three.

Anderson, a professor and researcher at the university and a mother of four, was arrested as she was leaving the building, Reyes told reporters Saturday. He said a 9 mm handgun was recovered from the second floor of the building late Friday.

Madison County District Attorney Rob Broussard said officials were considering other charges, including attempted murder. Authorities have not ruled out the possibility of other suspects in connection to the shooting.

Anderson, who is known to students as Dr. Bishop, had been working at the university since 2003, and was up for tenure, according to spokesman Ray Garner. However, authorities wouldn't discuss possible motives or whether the issue of tenure may have played a role in the shooting.

Garner told CNN that the university gives teachers six years to get tenure. Those who do not get it are terminated, he said.

University President David Williams said a prayer service would be held on Sunday. He said the campus would open next week for employees, but that there would be no classes.

Reached at the couple's home, Jim Anderson told CNN that his wife has an attorney whom he would not identify. He described her as a good teacher.

CNN's Alona Rivord, Aaron Cooper, Khadijah Rentas and Tom Watkins contributed to this report.