Birmingham closed one of its largest schools for a thorough safety sweep Thursday after metal detectors and other security measures failed to keep students from handling a gun in a classroom where one 17-year-old was fatally shot and another wounded in an apparent accident.



Birmingham Interim Police Chief Orlando Wilson said investigators are reviewing surveillance video for clues and interviewing students and staff to figure out exactly what led to Wednesday afternoon's shooting at dismissal time at Huffman High School.



"We consider it accidental until the investigation takes us elsewhere," Wilson said. "We have a lot of unanswered questions. There are so many unknowns at this time."



The gun was recovered, but Wilson declined to say who fired it. No arrests were immediately reported.



"We're hoping if we have footage, that it will reveal it," he said. "If we have witnesses, we're hoping they will tell it."



The two students weren't officially identified, but Birmingham Mayor Randall Woodfin said young woman killed was a senior, about to turn 18 and had been accepted at college, with "aspirations and dreams to be a nurse."



"We are not just talking about some person, we're talking about losing a part of our future. Our hearts are heavy," the mayor said.



The chief said he had not been told of any kind of argument, fight or struggle that preceded the shooting, which also wounded a 17-year-old junior on the football team, al.com reported.



"We're not saying he shot her, we're not saying he didn't shoot her," the chief said. "We're asking those questions ourselves so we can determine exactly what happened."



The shooting prompted a brief lockdown, with students and teachers sheltering in place. Wilson also confirmed that metal detectors were in place and functioning in the school. "This should not happen in schools," he said.



Birmingham City Schools Superintendent Lisa Herring announced late Wednesday night that school will be closed on Thursday, to give authorities time and space for a thorough security sweep and enable collaboration with community organizations to counsel students and staff.



"The magnitude of this event causes us to pause," Herring said. "However, we want to assure our parents, students, staff and community that safety and security are a top priority for Birmingham City Schools."



Security was being increased at all city schools. Just last week, as police and school officials investigated a reported threat at Huffman Middle School, a gun was found outside an entrance door, believed to have been left there as students prepared to be scanned and have their backpacks checked.



Gov. Kay Ivey said she's "praying for the family of this young lady who has tragically lost her life way too early ... it reaffirms that there is no place for students to have firearms or other weapons on campus."



The shooting happened the day after the Ivey created a school safety council to make recommendations on security in Alabama's schools, including updated threat plans and training for students and staff on emergency situations.



Alabama lawmakers have proposed multiple measures in response to last month's killings of 17 people in a Florida high school. Republicans would arm either teachers or volunteer security forces in schools. Democrats would limit or ban the sale of assault weapons. All these proposals face a tight deadline before the end of Alabama's legislative session this election year.