Prosecutors allege Jennifer Hudson's estranged brother-in-law killed three family members because he was angry the singer's sister was dating another man.

A Cook County prosecutor said at a hearing Wednesday that William Balfour came to the family's home the morning of the Oct. 24 killings and confronted Julia Hudson, his estranged wife and Jennifer Hudson's older sister.

The prosecutor says Balfour and Julia Hudson left together, but Balfour returned to the home, and the bodies of Hudson's mother and brother were found there later that day.

Prosecutors say Balfour that day admitted to the shootings and asked for an alibi.

View photos of the family and investigation

The body of Julia Hudson's 7-year-old son was found in an SUV three days later.

A former co-worker of Balfour's described him to FOXNews.com as a calm and polite man when he was a cook at a local restaurant in the South Side of Chicago. According to the source, Balfour was vocal about his relationship with Julia Hudson.

"After we got to know each other, he had shown me a picture of him and his girlfriend whom he told me was Jennifer Hudson's sister. I didn't believe him at first but after seeing the picture and the resemblence, I believed him," the co-worker said. "I was shocked when I learned [he was a suspect]."

A defense attorney says Balfour says he is innocent.

A judge denied bail Wednesday.

FOXNews.com's Allison McGevna and the Associated Press contributed to this report.