The source of "Mars was murdered"

I've tracked down the source of "Mars was murdered," the statement mentioned in "Arizona and the murder of Mars." It's in Whitley Strieber's book The Key (2001), spoken by the character I have identified with Tim, but whom Strieber calls the Master of the Key. He first says:

There was a war. Now the victors call earth "Dead Forever" because you are required to recur in the body until you are truly free. The wheel of life, as it is called by the Buddhists, is your prison. . . . When you see UFOs, you see prison guards.

When Strieber asks for more details about this war, he is told this:

Your species bears a wound in its soul that makes you deny the reality of the past that is plainly visible all around you. Mars was murdered by you. At that point, intervention occurred, as it will again when you destroy this planet, as will probably happen. This is the trigger for intervention, the destruction of a living world.

I thought I remembered the simpler statement "Mars was murdered," though, without the addition of "by you." I found this in a 2011 interview quoted in the book-length critique Problems with Strieber and The Key by Heinrich Moltke:

In 1985, October/November of 1985, 1 was discussing the Viking image of the face on Mars with Richard Hoagland, Greg Molnaar, Vince DiPietro, and a number of others. One of us, I don’t know which one, it wasn’t me and it wasn’t Richard, said in this internet relay chat we had — the internet was in its infancy then and it was a chat system I think that belonged either to NASA or to one of the universities that one of the participants in the conversation was at, said something extraordinary, he said: Mars was murdered.

He pointed out that the DNM [sic] pyramid had been entered at its base. There was a crater at its base that was an intrusion point. And you can see on the opposite side of the pyramid where something has caused it to collapse in on itself.

Now I’m going to go forward a bit. And I’m just piecing things together here, just little crumbs that I have. To a letter I received sometime after I published Communion, probably about six months. From a woman who had been walking in the woods with her little nine-year-old boy. And she wrote me because a dark blue figure like some of the ones I described in Communion had come face to face with her in those woods. He had come out of a cave, this small dark blue figure, and he spoke to her. He said that he was a rebel. And that there had been a war between earth and Mars before our history even began. And that both sides had lost in the sense that we had stripped Mars of its livability on the surface, but they had captured the human soul. And they now forced us to live in a perpetual state of recurrence, never making any progress. Dying, and then being reborn into the physical, and dying and being reborn into the physical, forever strapped to the wheel of life. And he said he disagrees with this and thinks that we should be let free. And he said his people call earth 'Dead Forever', that’s their name for it. [...] And I’ve wondered if those enigmatic statements by the Master of the Key don’t perhaps resonate in some way with this story.

Moltke comments:

In fact, the Master of the Key’s statements more than dovetail with the quoted stories. The Master of the Key explicitly draws on both episodes of Strieber’s life — his participation in the internet relay chat and his receipt and reading of the letter — by using the same two operative phrases, ‘mars was murdered’ and ‘dead forever’ verbatim. But rather than realize that he is drawing on his own experiences to create a synthesis that forms the true basis of the Master of the Key’s “enigmatic statements”, Strieber performs a subtle, slippery reversal making the source of those statements a posteriori supportive evidence for them.