What was the motive behind the shocking and brutal killings of Jennifer Hudson’s mother, brother and 7-year-old nephew? The man police call a “person of interest” in the case had been at odds with his ex-wife, the boy’s mother, and had threatened to kill her, a neighbor of the family tells Us.

William “Flex” Balfour allegedly got into a heated argument with Julia Hudson, her brother, Jason, and her mother, Darnell Donerson, about a month ago, regarding the sale of a car he and Julia co-owned, according to TMZ.