The police in Pennsylvania were building a case against her, and one of the key pieces of evidence--it's long and complicated, like every criminal case--was cellphone records proving that she was actually in Pennsylvania at the time of the killing. They had a lot of other evidence, but that nailed it down, and that took longer--that took well over two weeks--and she fled the country one week after the murder.
On March 16th, 2010. See this statement in context.