The Washington Post has an article published that takes a very detailed look at the Itaewon crowd crush disaster:

For nearly four hours before people started dying during a Halloween celebration in Seoul’s Itaewon district, partygoers pleaded with police to divert the crowds that were packing World Food Street and pushing into a 16-foot-wide alley — a tight, sloping space where most of 158 lives would be lost in a gruesome crush.
And once that crush began, it took at least 26 minutes for emergency personnel to start effectively evacuating people. Some victims were trapped for more than an hour before rescuers reached them. The delays proved catastrophic.
A Washington Post analysis of more than 350 videos and photos, some obtained exclusively and many reviewed by experts at The Post’s request, found that multiple critical factors contributed to the tragedy and death toll in Itaewon on the night of Oct. 29.
Washington Post
You can read more at the link, but really I only learned two new things from the article. First is that 119 calls were being placed about people being injured due to overcrowding in the alley almost four hours before people died. There was police officers there trying to redirect the crowd before the crush happened. However, there was not enough of them to stop more people from entering the alley.
What the article does not answer is who was the group reports claimed was pushing people on top of the slope? Was there really a Korean celebrity sighting that triggered the pushing? Hopefully someone figures that out because the alley was over capacity for almost four hours before the pushing caused it to turn tragic.