Why do people think Leopold and Loeb were gay?

I realize that Rope isn't directly about the murder committed by Leopold and Loeb, but since the killers in Rope were inspired by these real-life individuals, it influenced me to look them up online. Admittedly, I've only read their Wikipedia article thus far, but I was a bit surprised to see no mention of their alleged homosexuality in there. Particularly since every mention of Leopold and Loeb I've heard (since reading about Rope) has made comments on how these two men were homosexuals. Where is the evidence for this?

Now, don't get me wrong. I'm not directly refuting the claim. As I said, I'm rather new to the story. But while reading about them, I began getting the impression that perhaps this was just a rumor that's persisted for so long due to it having made an already interesting story even more interesting (especially for that time period). And now it's just being blindly accepted as a fact.

You see this type of communal reinforcement happen very often for a large variety of things, particularly in regards to popular news stories (to this day people mistakenly presume Anne Bony and Mary Reed were lovers), so it seems highly plausible that this could be what's happened in this instance, as well. I noticed when reading about Loebs death, at the hand of a fellow prison inmate, that rumors circulated that perhaps Loeb had put the moves on the prisoner. However, both Leopold and the prison's chaplain (who Loeb often spoke with) scoffed at this idea and I didn't see any other evidence that corroborated Loeb behaving in this way prior. This, though, was the only "evidence" of homosexuality that I'd read about. A rumor which the news, apparently, was quick to run with and spread.

As I said, though, I'm far from an expert on this topic. And I have zero stakes in whatever their sexuality is. I'm just curious, is all, about what the actual truth is and if there's any evidence that I've overlooked. Perhaps something was mentioned in court or in Leopold's autobiography?