Poor Madeleine! Did not deserve to die like that ;A; Unfortunately, I’d say she was condemned to die by proxy, being so attached to Claudia.

I don’t think Madeleine’s death was totally under Armand’s control. He was not really the leader of the TdV (see more quotes on that below the cut); in TVA Armand says: “For the record, [Claudia] was slain by my Coven of mad demon actors and actresses,… it became all too clear to too many that she had tried to murder her principal Maker, The Vampire Lestat. It was a crime punishable by death, the murdering of one’s creator or the attempt at it”

^“slain by my Coven” but not that he ordered them to do it. Just that he didn’t stop it from happening.

This is an #unreliable narrator situation again, as there are at least three different accounts of the trial that was held under TdV (see more below the cut)(four if you include the above statement from TVA). In all instances, the important part of the “trial” was that Claudia was the one who had to be convicted and sentenced to death. Louis and Madeleine were secondary concerns. 

There was no explanation for why Madeleine was also condemned to death, I would suggest that Santiago (and/or Armand) wanted to kill Madeleine bc she was mad (the extent of which we don’t really know) and/or they didn’t really know what else to do with her. Santiago probably wanted to do it bc it’s thrilling to kill another vampire, as Armand pointed out in book!IWTV: “`You see,’ he said, `killing other vampires is very exciting; that is why it is forbidden under penalty of death.’

1. Movie!IWTV – Armand is not part of the “trial,” we see him close the door against the whole scene, and he waits until later to free Louis from his (upside-down!!! SO MEAN) imprisonment in the walled-in coffin o’ doom. So one would guess that Armand at least negotiated w/ Santiago to have Louis’ life to be spared in this way.
2. Book!IWTV – Armand was not present at the “trial.” Santiago seemed to be the one running that show. 

   Again, one would guess that Armand at least negotiated w/ Santiago beforehand.

3. TVL – Armand was present at the “trial” and seemed to be the one running that show, and Madeleine is not even mentioned.

In movie!IWTV, we see Armand closing the door on the screams of the condemned, and the explanation as to why he didn’t come out to help when Louis called for him? He had told Louis that he wasn’t really the leader of this coven, “But if there were a leader, I would be that one.” 

In book!IWTV, similarly:

“ `Are you the leader of this group?’ [Louis] asked him.
” `Not in the way you mean leader,’ [Armand] answered. But if there were a leader here, I would be that one.’

Armand knows that to exert power, you have to defend it:

[Louis says:] “ `Stop them if you will, advise them that we don’t mean any harm.
Why can’t you do this? You say yourself we’re not your enemies, no
matter what we’ve done… ’
” I could hear him sigh, faintly. [Armand says:] `I have stopped them for the time
being,’ he said. `But I don’t want such power over them as would be
necessary to stop them entirely. Because if I exercise such power, then
I must protect it. I will make enemies. And I would have forever to
deal with my enemies when all I want here as a certain space, a certain
peace. Or not to be here at all. I accept the scepter of sorts they’ve
given me, but not to rule over them, only to keep them at a distance.‘ 

^Armand, IWTV