Three schools in Colleyville were under lockdown as police investigated an anonymous tip of "a potential school safety concern," according to the Grapevine-Colleyville Independent School District.
Colleyville Heritage High School, Heritage Middle School, and Heritage Elementary School were on lockdown starting around 3 p.m. Tuesday.
Both the middle and elementary schools were placed on lockdown due to "an abundance of caution." There has been no threat reported to either the middle or elementary schools, the district says.
According to the district, a student at Colleyville Heritage High School found an anonymous letter detailing a threat to the students. After the student took the letter to the main office, Grapevine and Colleyville police officers responded and had heavy presence.
A parent emailed a photo of the letter to NBC 5. Colleyville police confirmed the contents of the letter.
HMS students were released at the regular time of 3:25 p.m. High school students were released at 3:45 p.m.