The motive behind the shooting spree in Montgomery County, Pennsylvania, which claimed six lives and triggered a massive manhunt for Bradley William Stone, the suspect in the case, could be a custody dispute, according to The Mercury, a local news outlet. Stone and his former wife, Nicole, who was shot in the incident, had been fighting for custody of their two children.

Stone and Nicole reportedly got married in 2004 and filed for divorce in 2009, according to reports. Stone later married his second wife, Jen, in September 2013. He reportedly filed an emergency petition to modify the custody for their children as recently as Dec. 5. On Dec. 9, Nicole filed a counterclaim to the petition. A neighbor reportedly told The Associated Press that Nicole would frequently express her concern over the custody dispute.

"(Nicole) came into the house a few times, a few separate occasions, crying about how it was very upsetting to her," neighbor Evan Weron reportedly said. "She would tell anybody who would listen that he was going to kill her and that she was really afraid for her life.”

The 35-year-old allegedly carried out shootings in three homes in Montgomery County, northwest of Philadelphia, on Monday morning. Nicole’s sister, Patricia Flick, her sister's husband, Aaron Flick, and the couple's 14-year-old daughter, Nina, were killed during the first act of violence. Flick’s son, Anthony, reportedly received head wounds in the incident and was later airlifted to a Philadelphia hospital.

Nicole’s mother Joanne Hill and grandmother Patricia Hill were killed at their home in nearby Lansdale. Stone is then suspected to have killed Nicole at her Lower Salford apartment. Stone reportedly also abducted their children but later left them unharmed.

Bill Andrey, a close friend of Patricia Hill, reportedly said that the latter had hinted at concerns over Stone’s behavior.

“She told me that she was afraid that Brad was going to kill Niki [Nicole]. She actually told me that not long ago,” Andrey said, according to The Mercury. “From what I understand Niki was filing for sole custody of the children from Brad because she thought he was getting dangerous.”

Stone, who graduated from Souderton Area High School in 1998, was a former Marine and had also served in Iraq. People close to the family said that Stone suffered from post-traumatic stress disorder because of which he was discharged from the military, NBC Philadelphia reported. He had been charged with driving under the influence in 2013, 2003 and in 2001, The Mercury reported, citing court documents.