I'm pretty sure the accused are not composites or clones, and are thus actual individuals, not alleged ones. Similarly, the betting man would put his money down on the idea that the statements were not laundry lists nor love letters, and thus real, rather than alleged threats. Speaking in an older style of sentence analysis, one my audience would be familiar with, the writer would have done better to use alleged to modify the verb in the sentence, rather than the noun. "Threats allegedly made by individuals against the school" perhaps.
I am no longer sure we can say that this usage is wrong, however. I have lived through this change and I think I can understand some of it. People are petrified of falsely accusing someone, believing they can be sued later for asserting guilt. It used to be confined to newspapers and evening news, wanting to get the news out there fast, but mindful of possible modification or retraction later. Sometimes there are hoaxes, sometimes events are misunderstood, sometimes the wrong people are identified as culprits. "Alleged" was put in as a protective, cautionary modifier.
In only a few decades, it has gotten quite out of hand. Multiple "allegeds" are not uncommon in news sentences and statements by institutions. Even the head of the English Department at the school, while wincing at the imprecision of where the word is placed and cognizant of its traditional and preferred usage, might say "Can't you work a few more of those into the text? We don't want to get in trouble later."
"Alleged" has become something of an incantation, an anti-lawsuit rune, attached to controversial sentences. This will not be diminishing any time soon, and will likely increase. People might find it irritating or amusing - some of both for me - but the imprecision will count less than the need for spell-casting. Folks will just feel better having enough of them there in the sentence, and the language will change.
I would still consider it wrong usage at this point - but I am a dinosaur and my ear is not the same as the majority culture. I would prefer that schools err on the side of being dinosaurs as well, as it seems one way of upholding standards. But my preference there is culturally loaded, isn't it?
(Yes, I also note that it is a bit ambiguous whether "school" refers to the building or the institution, but it doesn't much matter.)
