Months after their son was shot and killed and the investigation didn’t lead anywhere, the mother took the case into her own hands and started looking for the culprit, authorities said.

The search ended when the mother shot a woman she mistakenly took for the person responsible for her son’s death, officials said.

A 65-year-old man from Norfolk, Virginia, and his longtime partner lost their son in March 2021 after he was shot and killed in Cleveland, Ohio, according to a news release from the U.S. Attorney’s Office for the District of Columbia.

The father told investigators he was “not satisfied” with the investigation into their son’s death and said his partner’s mental state had been “collapsing” since, according to court documents obtained by McClatchy News.

The man said his partner told him she would kill the person responsible for their son’s death if she ever found them, authorities said.

The man’s defense attorney did not immediately respond to a request for comment from McClatchy News on April 29.

During their investigation, detectives said they found a blue notebook with handwritten notes from the mother with loose pieces of paper covered with names, addresses, phone numbers, travel directions and other personal information.

The notes showed the mother planned to kill the woman she believed responsible for her son’s death and die by suicide, authorities said.

One of the notes stated: “Your dad will be with me but I am the one that will take her life,” court documents show.

In November 2021, the mother shot “Chelsea,” a woman she mistakenly identified as her son’s killer, authorities said.

On the night of Nov. 5, “Chelsea” was home cooking in her kitchen when she heard a knock at the door, court documents show. When she looked through the peephole, she saw what seemed to be a UPS delivery person who claimed to have a package for her.

When she opened the door, the mother, who was wearing the uniform, pointed a gun at her and shot her, authorities said.

The woman ran up the stairs to lock herself in a bedroom with one of her family members, yelling “I’ve been shot. I’m sorry I knew I shouldn’t have opened the door.”

The woman later told police the mother had spray-painted the word “PIG” on one of her family member’s vehicles months prior, court documents show.

During an interview with detectives, the father said earlier that day, he and his partner were sightseeing in Washington, D.C., authorities said.

The man said his partner then suggested visiting her friend “Chelsea,” adding that she had a package for her. When his partner got out of the car to drop off the package in question, he said he couldn’t see where she went — but heard two gunshots, court documents show.

Shortly after, the mother walked back to the car with the box still in her hand and told him “let’s go,” according to court documents.

The couple quickly changed their vehicle’s license plate from an Arkansas one to Virginia plates but were pulled over by police mere moments later after the man took an illegal left turn, authorities said.

“Chelsea” was taken to the hospital and survived her injuries, according to the release.

Days later, the mother died by suicide on Nov. 18, according to authorities.

Detectives said they found no information that suggested the woman was involved in the couple’s son’s death.

On April 29, the father pleaded guilty to accessory after the fact to assault with intent to kill, according to the release. His sentencing is scheduled for June 14.