VAN NUYS, LOS ANGELES (KABC) --Grant High School in Van Nuys saw heavy police presence on Tuesday after threatening messages were posted on Instagram.
The school, located in the 1300 block of Oxnard Street, was well surrounded by police officers even before classes began. In addition, more than a dozen officers were staged around the corner at L.A. Valley College.
Authorities said the school campus will be open Tuesday amid the increased police presence.
Monday morning, the school was placed on lockdown for several hours due to an online threat, which police later said was being investigated as an apparent hoax. The specifics surrounding this threat were not disclosed, with officials only saying it was communicated online.
Two students were detained - one of them were arrested. The lockdown was lifted late Monday morning.
Student Jason DeLeon said the student allegedly responsible for the initial threat was in his first period class.
"His facial expression is the same all the time, so you really can't say if he was sad, mad," DeLeon said.
Monday night, two alarming posts were published on Instagram via an account that has since been deactivated.
The first post showed an image of a bag that appeared to have wires and a timer inside. The user stated "I am not joking...see you tomorrow at 7:45am."
The second post showed the school's emergency evacuation route. The user asked for comments on which room to place the bombs.
The same Instagram user also referenced the earlier threat that prompted the Monday morning lockdown, stating "that was part of the plan."
The heightened security response included a mix of L.A. School Police, Los Angeles Police Department bomb squad members and K-9 units.
School police haven't said if the students had the means to carry out the attack but said after an hour-long search on campus on Tuesday, it was safe for students to return.
Investigators said they do not know the identity of the person responsible for the threatening Instagram posts. As for the student who was arrested on Monday, he or she can face a wide range of charges, including making criminal threats.
City News Service contributed to this report.