Editor's Note: An earlier version of this report incorrectly stated that .22 caliber shells were found in the bathroom. The school district originally said that shells were found, but a school district representative later said that bullets, not casings, were found. NBC 5 regrets the error.
Highland Park High School in University Park dismissed early on Wednesday after a .22 caliber bullets were found in a boys bathroom.
No weapon or note was found with the bullets. The school district at first said that a box of .22 caliber shells was found but later described them in a message to parents and staff Wednesday night as a "handful of .22-caliber bullets."
Principal Walter Kelly said in the statement that the school and law enforcement have determined that there was no legitimate threat to public safety.
Investigators gathered surveillance video from the bathroom where the bullets were found and interviewed several people.
No one has been charged in the incident.
Initially, school officials said students were not going to be dismissed and would be held at the school. One student was taken into custody by University Park police and returned to school after trying to leave campus. Police said the student is not connected to the bullets or the previous notes and was told to leave campus by his or her parents.
At 12:30 p.m., a decision was made to dismiss students at different times by grade level.
School officials released the following statement to parents Wednesday:
"We want to thank parents, students and faculty for their cooperation and understanding. Safety is always our top priority. HPISD will continue to update parents, students and staff through its emergency text-message system, email, and posts on the district website."
Parents waited outside the school Wednesday morning for their children. Many received text messages from their children.
"He was communicating for a while, back and forth," Michelle Bardwell said. "He didn't know what was going on. He said just that they were on lockdown, sitting on the floor."
The FBI and University Park police are investigating the incident.
The incident is the fifth security incident on campus in the last month. The campus was dismissed early Tuesday after a threatening note was found on campus. In January, classes were dismissed early twice after three threatening notes were found in a boys bathroom on consecutive days.
The box of bullets was not found in the same bathroom where the previous notes were found. If the incidents are connected, the person responsible could face felony charges.
While students' safety is the utmost priority, it is imperative to continue with classes, Kelly said in his statement. The high school be on its regular schedule Thursday and will have an increased police presence.
Because the bullets and the threatening notes were found in bathrooms, restroom access will be restricted.
"Students will only be allowed to use restrooms during passing periods. Those who need access to restrooms during class will be escorted by a staff member," Kelly said.
Students said they understand the reasons for the changes.
"It seems kind of funny having a teacher escort you to the bathroom, but I get why they're doing it, and I think they're doing the right thing," Katie Crow said.
"They're just trying to make everyone feel safer. And I sort of felt safe today, but just the fact that there were police and SWAT and lockdowns -- I was still really scared, so I think tomorrow it will make everyone feel better," Alex Cornett said.
Highland Park High again will only have two entrances open on Thursday. On Wednesday, the school closed all but front doors on Emerson Avenue and the student entrance on Westchester Avenue in wake of the threatening note found on Tuesday.
NBC 5's Ray Villeda and Amanda Guerra contributed to this report.