Good question...For Florida (and I'm new here, so I hope these links are acceptable sources):
http://statelaws.findlaw.com/florida-law/florida-first-degree-murder-laws.html
"For a charge of
first degree murder based on a premeditated killing, the prosecutor must show the defendant's specific intent to kill. The prosecutor often must establish an advance plan or design formed to carry out the homicide. To establish premeditation, the prosecutor may need to present evidence about the defendant's activities or steps taken to prepare for the killing." (Doesn't look like they have this evidence.)
2nd degree: No premeditation on JW's part.
http://statelaws.Florida state laws permit the prosecution of second degree murder when the killing lacked premeditation or planning, but the defendant acted with enmity toward the victim or the two had an ongoing interaction or relationship. - See more at:
http://statelaws.findlaw.com/florida-law/florida-second-degree-murder-laws.html#sthash.qmLrOHeM.dpuf
Manslaughter: Culpable negligence. KB didn't prevent it or report it, and engaged in drug use ("reckless behavior").
http://statelaws.findlaw.com/florida-law/florida-involuntary-manslaughter-laws.html
I think these charges are more likely to get a swifter conviction and max sentence with the evidence (and I'd rather see appropriate charges than an over-charge of 1st degree resulting in no conviction..... JMHO....).
Justice for Baby Chance
(Sorry for the multiple copy/pastes! Getting accustomed to a new laptop, Windows 10, and WS website... I think I should change my User Name to "JustTechnicallyChallenged".....GAHHH.)