harry potter - Did the students at Hogwarts know what Snape did at the end of Half-Blood Prince?

In addition to the answer above, I would point to the exchange between Lupin and the trio in Grimmauld Place, where they discuss the 'party line' on why Harry Potter is wanted. Lupin passes a copy of the Daily Prophet to Harry:

Harry smoothed out the paper. A huge photograph of his own face filled the front page. He read the headline over it:

WANTED FOR QUESTIONING ABOUT THE DEATH OF ALBUS DUMBLEDORE

Harry Potter and the Deathly Hallows - p.171 - Bloomsbury - chapter 11, The Bribe

And, even before that, there's the interview with Rita Skeeter:

'Well, I don't want to say too much - it's all in the book - but eye witnesses inside Hogwarts Castle saw Potter running away from the scene moments after Dumbledore fell, jumped or was pushed. Potter later gave evidence against Severus Snape, a man against whom he has a notorious grudge. Is everything as it seems? That is for the wizarding community to decide - once they've read my book.'

Harry Potter and the Deathly Hallows - p.29 - Bloomsbury - chapter 2, In Memoriam

So, as well as Rita Skeeter's tabloid journalism, there was an official effort to absolve Severus Snape of the crime. So, anybody who followed the official, government line (or whose parents followed it) would certainly have been made to doubt that Snape was responsible.

At the same time, Skeeter acknowledges the 'theory' that Snape was the murderer, so anybody who read that interview in the Prophet would have certainly heard that rumour. And the way she talks about it casually makes it sound like it had been 'doing the rounds'. However, it does seem that she goes on to doubt it.

So, I think the answer is that most people would probably have heard Snape blamed for Dumbledore's death. But there was a real and concerted government effort to transfer blame away from him. And then there was Rita Skeeter's meddlings. Exactly what average Joe Hogwarts student thought is hard to say. Given the events of The Order of the Phoenix it's not hard to imagine plenty of people having their doubts that Snape did it. But at the same time I've little doubt the DA, all Gryffindor seventh years and plenty of others believed it was Snape.