A 71-year-old Florida man, who served 15 years in prison for killing his estranged wife, confessed Wednesday to stabbing his 42-year-old roommate because he has "a hard time being rejected,"according to a Bradenton newspaper.

Warren Birkbeck, who was sent to prison in 2000 and paroled in 2015 in New Hampshire for the 1999 stabbing death of his estranged wife, was living with the 42-year-old victim and another woman in Holiday on Florida's Gulf Coast when the stabbing occurred early Wednesday morning hours.

He told authorities after his arrest that he became upset when he overheard the victim, Denise Cook, talking to a man on the phone. He barged into her bedroom, and grabbed a knife after she told him to leave, the Bradenton Herald reported.

Birkbeck stabbed Cook "approximately three to four times in the chest," according to the arrest affidavit. When asked by authorities why he killed Cook, Birkbeck told police: "I just have a hard time being rejected."

He reportedly told a 911 operator: "I just had to. I just flipped out tonight and I ended up killing her."

Birkbeck was on probation until 2029 in the second-degree murder of his estranged wife. He was also convicted of manslaughter in Massachusetts in 1962, according to New Hampshire news outlets.

Neighbors told Bay New 9 that they had no idea of Birkbeck's background. "It's just shocking because you never know who's living right next door to you," one said.

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At the crime scene Wednesday, Pasco Sheriff Chris Nocco held a press conference, lamenting the "horrific day" for the victim's family. "We just hope that people pray for her."

As for Birkbeck, the sheriff said: "No other way to say it. He's a killer."