Students were released from classes on time from three Colleyville schools that were in lockdown Tuesday afternoon while police investigated an anonymous tip describing a possible threat to safety at Colleyville Heritage High School, officials said.Police lifted the lockdown and classes were released at the normal time of 3:45 p.m., said Megan Overman, spokeswoman for Grapevine-Colleyville School District.Officers were on hand, but there was no apparent panic; students were seen leaving in an orderly manner.Police were still investigating the threat which came in the form of a note, but other details were unavailable late Tuesday afternoon, said Mona Gandy, Colleyville police spokeswoman.In e-mails to parents, CHHS Principal Joe Harrington said a student found an anonymous note in the cafeteria during lunch and immediately brought it to the front office."It contained a very vague threat against Colleyville Heritage," Harrington wrote. "We immediately contacted Colleyville police. They dispatched extra officers and began working with us to thoroughly investigate the situation."At first, police did not believe this to be "a credible threat that would warrant a lockdown."But in a later e-mail, Harrington said officials called for the lockdown a few moments before 3 p.m. "as a safety precaution.""A student reported additional information concerning the anonymous threat that was found at lunch," he said.The lockdown began at about 3 p.m. and lasted for about 45 minutes, Overman said.According to a statement on the CHHS website, police said the lockdown was ordered out of "an abundance of caution.""In that same abundance of caution, the district has placed nearby schools Heritage Middle School and Heritage Elementary School on a temporary lockdown as well," according to the statement.The information also noted that "there has been no threat reported to either HES or HMS." Also, students at those schools were also released on time."Both Colleyville and Grapevine Police have increased their presence in the area and district leaders will continue cooperating fully throughout the investigation," according to the statement.The lockdown at Colleyville schools followed a similar incident Tuesday morning at Lamar High School in Arlington.A lockdown there was ordered for more than three hours after a student told a school resource officer that a classmate may have brought a handgun to school. Police searched but no gun was found and the lockdown was lifted during the lunch hour.