Killer grandmother reveals in chilling seven-page letter to cops why she gunned down her son's ex-girlfriend as she loaded her one-year-old baby into a car in posh NYC neighborhood

A terminally-ill grandmother who fatally shot her son's ex in a grisly murder-suicide detailed allegations of abuse in a seven-page note.

Kathleen Leigh, 65, claimed that her former daughter-in-law Marissa Galloway, 45, tried to alienate her four-year-old daughter from her son - the girl's father - in the note found in her pocket, sources told the New York Post.

She also wrote that no one believed her and her son's claims that Galloway abused the young girl - an accusation New York City's child service investigators twice determined were unfounded.

The letter - scrawled with the words 'For Police' - was found on Leigh's body after she shot Galloway in the head and back as she was loading her one-year-old into a car seat in the back of a parked vehicle on the Upper East Side Friday morning.

Leigh then took her own life by shooting herself in the head, police said. 

Kathleen Leigh, 65, pictured in surveillance footage from the shooting on Friday, claimed in a seven-page note that her former daughter-in-law was abusive to her four-year-old granddaughter

Leigh shot and killed Marissa Galloway (pictured), the mother-of-two, on a Manhattan street Friday morning before taking her own life

The four-year-old, who was not with her mother or grandmother at the time of the shooting, had been the subject of a years-long custody battle between Galloway, a special education teacher, and Leigh's son.

Over the course of the battle, both sides have accused the other of child abuse, according to the Post. 

In some of the reports, the girl's father would claim that his daughter would arrive home with bruises on her arm, but investigators found the accusations unfounded. 

Leigh had even brought the claims to her neighbors in a Manhattan apartment building, where she has been living for the past three years with her son. 

Galloway had been loading her one-year-old daughter into a car seat in the back of a parked vehicle when she was shot

'She always talked about the fact that she had a former [partner] that was harassing the hell out of her because I had child services at my door one evening asking if I had ever heard any problems next door,' said neighbor Meryl Feidelman.

'I said, "No, no she's a lovely, lovely mother, a lovely woman."'

But Galloway also had a history of domestic violence disputes with her partner related to the custody battle, according to NYPD's chief of detectives Joseph Kenny. 

Five reports and two complaints had been filed with the NYPD between July 2021 and November, but no arrests were made.

Galloway has been battling custody of her four-year-old child with Kathleen's son, the father of the child, since 2021. The one year old does not belong to Leigh's son

The child is now in the custody of Leigh's son, as the NYPD continues to investigate the murder - which occurred just steps away from Mayor Eric Adams' residence.

She had been with her father when her grandmother murdered her mom along the usually quiet tree-lined street just before 9am.

Two guns were recovered at the crime scene - a 9-millimeter gun from the sidewalk and another gun in the Target bag Leigh had on her. 

Police are trying to confirm whether or not Leigh had owned the firearms during her time as a probation officer in Chicago - where she worked for 17 years before retiring in 2014.

But officers believe she acted alone in the killing, and have no evidence that her son knew of her plans, according to the Post.

Still, Galloway's family could have standing for at least some custody of the four-year-old under special circumstances that would be met 'when the mom is murdered in cold blood,' a custody lawyer told the Post.

Her other child - a one-year-old girl whose father was reportedly a sperm donor - is now with her maternal grandparents in New Jersey.