That was my post earlier. The problem is, it isn't really an "upgrade" to malice murder from felony murder. The charges carry the same punishment (for the triggerman) in Georgia, and felony murder is not a lesser included offense to malice murder.
What is different between the two charges is the underlying elements of the crimes involved. For a probable cause affidavit for felony murder, you are going to have to show to a judge facts that are sufficient to show probable cause that a separate felony had been committed, and also that it was because of and in the course of that felony that the death occurred.
And as the arrest warrant stands now, there is nothing in it that gives probable cause that McD committed any other felony, or that Lauren died during the course of it. It's just not there. Having a master key to the apartment complex is suspicious, but almost certainly falls below the threshold of reasonable doubt to believe that McD committed some specific felony crime. And it is definitely short of proving that Lauren died during the course of the felony, when there is no clue given as to what/when/where that felony was, or how McD killed her during the course of it.
It could very well be that the LE/DA are trying to play both sides of the fence here, and that they are being deliberately ambiguous about what McD has actually been arrested for. But that's a dangerous game, and it can't last for long. It is impossible to sustain a conviction for both malice and felony murder with the death of a single victim. And when the indictment comes out, the DA will have to make a final decision about what charges it wants to pursue, as shown in Wagner v. State, 282 Ga. 149, 646 S.E.2d 676 (2007) -- which holds that an indictment failing to differentiate between malice and felony murder is fatally defective. (Note that this does not preclude bringing both charges in the alternative. But it does require specification as to which is charged.)