Nathan Leopold's fascination with the poems of Laurence Hope emerged during the highly-publicized Leopold and Loeb murder trial of 1924. The world was fascinated by the apparently unmotivated crime by two supposedly brilliant University of Chicago students, and Clarence Darrow's eloquent efforts to save the defendants from the death penalty. Extensive psychological testimony centered on Leopold's sexual attraction to Loeb. At one point during the trial Leopold responded to a reporter's question about his attachment by saying "I feel myself less than dust beneath his feet. I am jealous of the food and water he takes because I cannot come as close to him as food and water do."
The subject of Laurence Hope's poetry came up during the trial itself on August 4, 1924 during the testimony of Dr. Healy, one of the psychiatrists who had examined Leopold. After Healy described Leopold's abnormal interest in crucifixion and "the idea of somebody being tied or he tying someone," he went on to describe Leopold's fascination with master / slave relationships. The following is from the trial transcript excerpts:
And he went on and told me, at great length, and elaborated freely upon the theme that he had first developed with Doctors Bowman and Hulbert, namely, the theme of the king-slave phantasy, which he began, evidently very early in life, and which has some very strange components of a childhood and abnormal nature, of which I have spoken in this, because that was not open to the public. The slave would be a person that would be made to suffer, but he would be a good looking, strong man in some ways. Saving the life of the king he would be offered liberty, but he  would refuse his liberty. Sometimes he himself would be the slave, and sometimes he would be the king.
As time went on, he belonged to a caste of slaves, a class of slaves; he himself was bound to his king by a golden chain, which he could easily have broken. He explains this by saying it was a vestigial remnant; his slave was as really as good as any kind. At other times he has phantasies about a boy being captured and beaten, and the king saves his life; or himself as a slave being stolen by gypsies, and brought up subject to punishment; or a boy who is captured in war time, and beaten, but saved by a nice young girl; all through there are these continual croppings up of suffering of causing to suffer in these phantasies. This imaginary life was developed very early, and had all along this abnormal material, and it kept up even last year. He has told us about this himself, and his aunt tells me that notwithstanding his tremendous activity and vigor, she had noted that sometimes during the last year he came in and went and lay down on the couch, and she supposed he was taking a nap, but these were the periods when he says he voluntarily  went into periods of day dreaming. These phantasies apparently have had an immense influence upon his life. They have come up again and again, and have had relationship to his relations to Loeb, and to other boys earlier. Normal phantasies, of course, are carried out with all of us in our ambitions, and in our interests in general. This boy carried his abnormal phantasies very early over into real life. He distinctly remembers, he tells us, even at twelve years of age, identifying a camp counsellor as a slave, and putting him into this position of slave-knighthood. Other boys are gradually drawn into this slave idea; any boy who would appeal to him as good looking was eligible for playing the part of his phantasy life; and he tells us of elaborating a scheme of capturing these, and even of branding them; he had a special sort of imaginary and complicated brand, which he applied in his phantasy to the inner calf of the leg. Most significant, according to his own account of his life, is the fact that three or more years ago, soon after their first acquaintance, Leob began to be woven into his phantasy life. Loeb would figure sometimes as the king, and sometimes  as the slave, but it was a transfigured Loeb. Loeb would be an ideal man, wonderfully good looking, an athletic star, a brilliant scholar, a fellow who got the highest marks in college. Now he knew none of these things to be true, but he forcibly transformed Loeb; he tried to make himself believe these things, and he himself says that he told many others about his admiration for and belief in Loeb; and from one of the boys' acquaintances I have confirmation of that fact. It seems to have been really a rather extorious [?] fact, that Loeb himself object to, that he was so continually praising Loeb and putting him on a pedestal. Dr. White told you about his stating that he made a chart of the perfect man, in which Loeb ranged much higher than himself. But it is also interesting to note that Leopold himself speaks of having made a complete identification of himself with Dick. Now, to this point we have the fact that Leopold is able to recite poetry at great length, and that in itself is an interesting thing, it seems so incongruous. All at once he is able in prison to declaim poetry, some three or four pages, which he dictated to me as fast as I could get it down.  The other day in the court room he passed me a little memorandum, and said this was the part of the poem that he had in mind particularly, one of Lawrence Hope's poems that he recited to me, and which I will give you a large excerpt from it you want it. This is what he wrote the other day, in court, and passed on to me:
"Let me dream once that dear delusion
that I am you,
O heart's desire."
And he prefaced it by "In re Dr. White's remarks about identification with alter ego, Dick; see poem I quoted to you." That line comes in this stanza,--it is hardly worth reading the whole poem: This is what he quoted with a good deal of apparent feeling, to me:
"Long past the pulse and pain of passion;
Long left the limit of all love'
I crave some nearer fuller fashion,
Some unknown way, beyond, above;
Some infinitely inner fashion,
As water with water, flame with fire.
Let me dream once that dear delusion
That I am you, O heart's desire."
MR. CROWE: Q Who is the poet that wrote that?
A Lawrence Hope, he tells me. I am not familiar  with it. I am informed by one of my confreres, however, that that is the fact. In his phantasy there was a ready changeabout of himself with Loeb and he fitted into Loeb's suggestion about their criminal activity because he could work out his double-faced scheme, the phantasy scheme of being either a king or a slave.
Bearing upon this whole problem of his phantasy life and upon his delusional tendencies, his ideas of superiority, and a fact that seems to be very well substantiated from his relatives, is that for many years he showed an abnormal and intense energy. Many witnessed that. He is never idle a minute. He has no ordinary fatigue. He would remain up all night when he was going to undertake some special task or investigation next morning often, because he thought he could do it better if he remained up.
As we know by his actual productions, he has been continually reaching out for new subjects to study,a and a developed formidable list. In his room he has an ornithology collection, which I have seen, which is really very remarkable. I do not know the exact number of birds in it, but a lot  of very rare specimens; but I think they stated there were something like three thousand specimens in the collection. (Source link)
In his autobiography, Life + 99 Years, Leopold noted singing "Less than the Dust" in his prison cell.