Police say they are continuing an "extremely complex" investigation into threats of a massacre at a Blackpool school.
A number of Facebook and Reddit messages on December 30 and 31 described plans to "kill as many people as possible" at Montgomery High School in Bispham on Monday.
The social media poster said the attack would be in revenge for alleged bullying.
In the messages they praised gun killers in schools in the United States and posted: "Nobody talks to me or notices me except when they're calling me a nerd and pushing me around."
When challenged by one student, the person replied: "You think it's a joke? You'll see bullets, bodies, and blood."
The school opened as planned on Monday after police ruled the threat was "not credible". The day passed with no incident as police officers provided a visible presence on site but many parents chose to keep their children away.
That night a futher post on the Blackpool Gazette newspaper's website by a user named 'The Real John Smith' claimed they were the person responsible for the original comments and apologised for their actions, said Lancashire Police.
The senior investigating officer, Detective Chief Inspector Gary Brooks, said: "This is an extremely complex investigation further complicated by the vast, global nature of the internet.
"Whilst the public can't visibly see what we are doing, I must stress that we have a dedicated team of officers and specialist resources working behind the scenes to identify who posted the threats and the subsequent 'apology' on the Gazette's website. Complex inquiries of this nature could take some time to complete.
"We are still of the view that the threat was not credible and we do not believe that any staff or pupils are at immediate risk of harm as a result of the posts."
He added: "We are treating this new post as a valid line of inquiry and it may well be linked to the original comments but it's still too early for us to say.
"The person responsible for the original posts may not have realised the seriousness of their actions and the extent of disruption they would cause. I would urge them to come forward and identify themselves. We will continue our inquiries until we trace this person.
"The school is open and we will continue to provide a visible presence."
School principal Tony Nicholson said the school was "rapidly returning to full capacity".
Anyone with information that could assist police with their investigation should call Lancashire Police on 101 quoting incident reference 0006 of December 30 2015.