the reason why manslaughter was not allowed for the first case was because the prosecution didn't lay a proper foundation to include the lesser charge of manslaughter.
the difference between murder second and manslaughter is the degree of the mens rea element.
within the last year, there were three cases that addressed the inclusion of the lesser charges these cases were Adviento, Flores, and Kaeo. In all three cases, the Supreme Court held that, if the difference between the charges are a difference in degree of the elements, and the facts support the lesser charge, then it should be included. When Deedy was tried the first time, these cases did not exist, so it was up to the discretion of the Judge Ahn. In this second trial, Judge Ahn is almost required to give the jury instructions for the lesser charges.
State v. Adviento, 132 Hawai'i 123 (2014)
State v. Flores, 131 Hawai'i 43 (2013)
State v. Kaeo, 132 Hawai'i 451 (2014)