Armed police were sent to a Merseyside school over claims a man threatened to kill there.
Officers were called to St Aelred's Catholic Technology College in Newton-le-Willows on Friday morning.
Staff and pupils were told to stay inside the building for nearly two hours and all entrances and exits were sealed while police investigated.
A 19-year-old man was arrested and a computer and imitation firearms have been seized from his home.
The alarm was raised after a threat with a picture of a gun was posted on the social networking site Facebook.
It is alleged to have been posted by a former pupil who claims he was bullied.
Parents arrived at the school, on Birley Street, after distressed pupils called them on their mobile phones.
More than 1,000 students were inside the school at the time of the alert, some of them taking their GCSEs.
A Merseyside Police spokeswoman said: "Officers were made aware of threats to the college in the early hours of this morning and appropriate measures were put in place.
"A 19-year-old man from Newton-le-Willows has been arrested on suspicion of threats to kill."