Once you're acquitted of a crime you can't be retried.
Double jeopardy
Actually....that is not entirely true. In the event there is dual jurisdiction whereby one could be tried for a State AND Federal crime (because the criminal act actually was both).....then you can be essentially re-tried for the same set of criminal facts and circumstances. For instance, say you murdered a Federal employee in Iowa. Iowa could try you or the feds could since murder is a state crime....plus killing a federal employee is a federal crime. Say Iowa tried you and you were aquitted......the feds could turn around and actually retry you for the same murder. Now murder isn't per se a federal crime....only killing a federal employee.
A real life example would be back in the civil rights era where a number of southern rednecks and Klansmen killed people only to be aquitted by all white juries. The feds went ahead and tried them again many times for the federal crime of violating their civil rights....and many times they were convicted in the Federal trials.
Sooooo, though in this case, I know of no federal crime that was committed that she could be tried for, so Casey can not be retried for anything, HOWEVER, as I already stated, in cases where there is dual jurisdiction (where a State and Federal crime was committed in the same criminal act), you can indeed be retried with no violation of the principal of double jeopardy as spelled out in the 5th Amendment of the United States Constitution.