By Jill Smolowe
Updated February 14, 2011 12:00 PM

Not long ago, Calyx Schenecker, 16, returned from a shopping expedition near her home in Tampa with a new pair of shorts. “They were the shortest things ever, like you could see her butt sticking out,” says Cathy Vann, a friend of Calyx’s mom, Julie. “Julie was like, ‘I hope you saved your receipt because those are going right back.’ ” Calyx’s response? “She was stomping around the house, screaming, ‘You’re jealous that you can’t wear these,’ ” says Vann, who witnessed the fight at the Scheneckers’ 3,300-sq.-ft. home in the upscale Ashington Reserve gated community. And Julie? “She gave as good as she got, saying things like, ‘People are going to think you’re a slut.’ ” Yet Vann was hardly shocked. “Every mom of a teenage daughter has these fights,” says Vann. “That’s why I was surprised that it ended like it did.”

On the morning of Jan. 28, police found Calyx slumped near her computer in an upstairs bedroom, her face and head fatally pierced by two bullets. In the garage her brother Beau, 13, was found in the family SUV, also dead from two bullets to the head. Schenecker, 50, clad in a blood-soaked robe and slippers and sitting on the porch shaking violently, told police that the prior evening she had killed her children-Beau on the way home from soccer practice, Calyx while she was doing homework-with a .38-caliber revolver purchased five days earlier expressly for that purpose. Why? Because, said police spokeswoman Laura McElroy, “they talked back, they were mouthy, and she was tired of it.”

Inside the house police found a note, penned by Schenecker, that detailed her plan to kill her children, then herself. Arrested and charged with murder, the stay-at-home mom was taken to the intensive care unit of Tampa General Hospital for treatment of a condition that investigators declined to disclose. (Earlier that day police had been told by Schenecker’s mother-who had phoned from Texas, concerned when her daughter didn’t answer the phone-that Schenecker might be depressed.) Half a world away her husband, Army colonel Parker Schenecker, 48, an intelligence officer on temporary assignment in Qatar, was informed of the tragedy. At a brief court appearance on Jan. 31, Schenecker was remanded to a county jail without bail. “We’re just in shock,” says Vann. “She’s so controlled usually, not the type to lose her temper.”

Yet clearly tempers had flared in recent months. According to a police report, Calyx began getting counseling at a local crisis center in the fall after she was slapped by her mother for being rude. In November a police officer and a state Department of Children and Families (DCF) representative visited the home after Calyx complained to her counselor of a new incident during which Calyx called her mother “disgusting,” and Julie responded by backhanding her daughter in the face several times. The officer determined there was “no evidence of a criminal offense.” A DCF investigation, which concluded nine days before the killings, noted that Beau “said that he feels safe in the home”; that the family’s therapist “had no safety concerns for the children”; and that dad Parker, who often plays “peacemaker in the home,” had none either.

Among her peers, Calyx was perceived as bright and popular. “She was one of those people who had a lot of friends,” says Kayla Collier, 17, a 10th-grade classmate at King High School. Enrolled in a pre-international baccalaureate program, “she was very mannerly, just a good all-American kid,” says principal Carla Bruning. Beau, a goalie on the soccer team at Liberty Middle School, had in recent months discovered porn on the Internet, says Vann. But still, “no red flags,” she says. “She had two teenagers. That just comes with the territory.”