"A $500 withdrawal ... every day," said Rott.
The pair holed up in a hotel room in San Antonio, shooting drugs day after day, month after month.
"She never left that room one time," said Rott. "The whole, over-nine-month time, the only time I ever left was to get food or drugs."
Her parents thought their daughter might be lost for good.
"We didn't know if she was alive," Tom Dick, Christine's stepfather, told ABC.
She stayed in the room until the police came for her.
"It almost looked like a murder scene inside this hotel room," said Harris. "There's blood on the wall, hundreds of needles, used needles on the ground, boxes of brand new needles ready to go and then, literally, about 80, 85 needles lined up on a dresser with heroin inside 'em. It reeked."
After the July 2006 call from the tipster, the police investigation advanced on two fronts. Using bank records, detectives were able to track Christine to her San Antonio drug den, where they arrested her.
Then they began to unravel the mystery of the second perpetrator, "Chris."
In video of a police interrogation of Christine, her fear of "Chris" is palpable.
"You're sure he's not going to be able to get me in here right?" she asked the detective questioning her. "Promise me that."
It turned out that "Chris" was Chris Snider, whom Christine had dated in the year leading up to the murder. Snider was a loner, about two years older than Christine, who had done jail time for armed robbery. According to Christine's parents, he was very controlling and he resented her female friends, including Rachael and Tiffany.
During her police interrogation, Christine said she was eventually able to get Snider out of her life and she had no idea where he had gone. The police, however, were already on his trail.
The tipster, whose identity was never disclosed, had told police the murder weapons belonged to Snider's father. Police executed a search warrant on Snider's parents' home in Kentucky.
"Lo and behold, in the father's bedroom was a little gun safe," said Harris. "And in that gun safe were the murder weapons." Detectives then used Snider's MySpace page and phone records to track him to Greenville, S.C. But Snider learned about the manhunt before they arrived.
The police found his body in the woods.
"He committed suicide," said Harris. "Overdose. Which is kind of ironic, for this big tough guy who brutally slaughters -- these four high school kids. He went out the coward's way."
Christine, now 20, blamed Snider for the crimes. The state responded by charging her with first-degree murder.
Rachael Koloroutis' family was shocked anew when they learned that one of her high school friends had been arrested and charged in the crime.
"I just remember sitting in my car and just shaking," said Tiffany Koloroutis, the elder of Rachael's two sisters.
After all, why would Christine want to kill her own friends?
Police had long suspected that drugs had played a role in the quadruple murder. They had discovered early on that despite its tame exterior, Tiffany's house had become a teenage hotspot.
"We learned that there was drugs that were sold from that residence and that these kids were involved in drugs," said Harris.