FYI a murder trial "with special circumstance" is only a trial and possible punishment for the murder that was committed, and not for the special circumstance crime, such as kidnapping in this case. The special circumstance is only a definition of the context framing the murder itself.
Therefore it would not violate double jeopardy rules to try EA for capital murder, after first having completed a trial for AK. Nor would it violate double jeopardy rules to try EA for kidnapping AFTER a capital murder trial, if they preferred to do it the other way around. They are two distinct crimes.
And not only would it be legally allowable to later try EA for capital murder, it might even be beneficial to do it this way. Two trials are more costly and more time consuming, so this is probably not the norm, but slow methodical tightening of the noose step by step is the surer way to get the needed result. By having kidnapping already adjudicated and proven, in court, it would leave LE one less thing to prove in the murder trial. In that event, besides the fact of EA committing the murder itself, they'd only have to prove that the murder flowed from the kidnapping that EA had already been proven to have committed.
Perhaps the AK trial is laying some groundwork for a future capital murder case and a shot at death for EA? If EA doesn't wise up and swap talk for a limit on punishment, we may eventually find out.