The police knew "that a large crowd had gathered even before the accident occurred, reporting danger urgently", acknowledged the national police chief Yoon Hee-keun.
But he considered "insufficient" the way in which this information had been treated.
At least 156 people, mostly young people, were killed, and dozens injured, in a crowd on Saturday night during the first Halloween party since the pandemic in Seoul's cosmopolitan Itaewon district.
About 100,000 people were expected, but due to the unofficial nature of the event, neither the police nor the local authorities actively managed the crowd.
Police acknowledged on Monday that they only deployed 137 officers to Itaewon on Saturday evening, while stressing that this figure was higher than those for Halloween parties in previous years.
Meanwhile, 6,500 police officers were mobilized for another demonstration in the South Korean capital in which only 25,000 people participated, according to local media.
The South Korean security forces are masters in crowd control, in a country where the numerous and frequent demonstrations are often supervised by a number of agents greater than that of the participants.
But in the case of the Halloween festivities in Itaewon, there was no designated organizer.
Partygoers gathered in the neighborhood to attend different events in bars, clubs and restaurants.
South Korean President Yoon Suk-yeol said on Tuesday that his country must urgently improve its system of managing large crowds following the disaster.
"People's safety is important," he said, "whether or not there is an organizer at an event," he told a government meeting.
Mr Yoon called on the country to acquire "advanced digital skills" to improve its crowd management.
But observers have said that these tools already exist and have not been used in Itaewon.
- The disaster could have been avoided -
Seoul City Hall has a real-time crowd monitoring system that uses cellphone data to predict the size of an event's attendance, but it was not used on Saturday night, according to media reports. local.
Itaewon district authorities also failed to deploy security patrols, with officials saying the Halloween event was considered a "phenomenon" rather than a "festival", which would have necessitated a official crowd control plan.
That night, tens of thousands of people rushed into a narrow alley.
Eyewitnesses described how, with no police or crowd control, disoriented revelers pushed and shoved, crushing people stuck in the alley.
According to analysts, this situation could have been easily avoided, even with a small number of police officers.
"Good and safe crowd management is not a question of ratio, but of crowd strategy - for safe capacity, flow and density" of crowding, said G. Keith Still, professor of crowd science at the University of Suffolk.
For South Korean expert Lee Young-ju, if local police knew they would be short-staffed, they could have asked local authorities, or even residents or shop owners, for help.
"It's not just the numbers," the professor at Seoul University's fire and disaster department told AFP.
“The question is how did they manage with this limited number (of police officers) and what kind of measures they took to compensate” for the lack of personnel, he estimated.
The day after the tragedy, criticism rocketed on social networks against the authorities, accused of lack of anticipation.
Many users accused the police of completely failing to control the crowd, leaving too many people to crowd around Itaewon subway station and in the alleys where the deadly stampede occurred.