Drew, Stacy's sister spar on WLS radio

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Drew Peterson's last morning radio appearance apparently was too much for the sister of missing mom Stacy Peterson to bear.

Stacy's sister, Cassandra Cales, called into the Mancow Muller show on WLS-890 AM radio Wednesday and lit into Drew Peterson, calling him a killer in a profanity-punctuated tirade.

"You killed her after she got off the phone," Cales barked at Peterson. "You will pay. I know what happened, I told the state police. Drew knows. It's not for the public's eyes. The truth will be told in court."

Peterson has not been charged in connection with the disappearance of Stacy, his fourth wife, in October 2007. Stacy reportedly last spoke with a mutual friend of hers and Cales on her cell phone just before she vanished.

Peterson, who has maintained throughout that his wife ran off with another man, has been a regular guest on the Mancow show over the last few months. But Wednesday's appearance veered from the usual light-heart banter between the host and Peterson.

The exchange between Peterson and Cales was taped Wednesday and aired this morning.

Besides accusing Peterson of murdering her sister, Cales accused Peterson of keeping Stacy's young son and daughter away from their Aunt Cassandra.

Peterson denied this as well, and claimed he does not want the children around Cales because of her poor driving record. He also explained that Cales was involved in a high-speed chase during which the police "had to Taser her down to bring her to justice."

Cales laughed this off and returned to calling Peterson a killer, and possibly worse, before hanging up the phone.

"My friend talked to my sister at 10:15 a.m.," Cales said. "She was laying in bed, and Drew wasn't in bed. Where were you Drew? You killed her after she got off the phone you piece of (expletive)."