Williamson, California, schools are on lockdown for the holidays, as students and parents return home following a devastating school shooting at an elementary school.
More than 20 people were killed and dozens more wounded during a gunman who was armed with a rifle and handgun, according to authorities.
Authorities on Friday said they were working to determine whether the shooter was related to the shooting, and were also searching for additional suspects.
Students and staff from schools in the community of Huntington, north of Los Angeles, were sent home Thursday after school officials closed two schools for the holiday.
The Williamson High School in the town of Huntington was also closed because of the threat, officials said in a statement.
Williamson schools were also closed in the Huntington-area of California on Friday as authorities searched for a suspect.
The lockdown was lifted Friday afternoon after a school district spokesman said he was confident that students would be safe in the area.
The district did not say if any students were injured during the lockdown.
The shooting happened at the Huntington Junior High School, where two students and two adults were killed.
School districts across the country are also being targeted by threats in recent months.
Authorities are also trying to determine how many students were in the school and whether they were also at the elementary school where the shooting occurred.
The FBI said Thursday it had taken in students who were at the school at the time of the shooting.
Authorities also said the shooter’s parents were located in Huntington.
Authorities released the names of those who were injured.