Peter O'Connor, a supervisor with the Bureau of Alcohol, Tobacco, Firearms and Explosives, said investigators had finished going through about half of the fire scene without seeing any signs the blaze was intentionally set, but they had yet to determine its cause.
City fire inspector Richard Linn said officers were seeking tips from anyone who may have seen or had contact with the four victims, all freshmen who lived in the same dormitory at the Mississippi University for Women in Columbus, Miss.
"We are trying to get the full story of what happened the last 48 hours of their lives," said Linn.
Fire broke out in a two-story Days Inn motel in suburban Birmingham Saturday night, spreading quickly through the wood-frame structure. The blaze killed 18-year-old cousins Alondan "Angel" Turner and Catherine Ann Muse of Cordova; Jamelia Brown, 18, of Grenada, Miss.; and Jaslynn McGee, 19, or Corinth, Miss.
Officials said someone from the students' second-story room called 911 to say they needed help, but the door and window were blocked by flames and firefighters couldn't get to the victims in time to save them.
A spokesman for the Hoover Fire Department, Rusty Lowe, said the room had smoke detectors but lacked a sprinkler system. The motel was built in the 1960s before sprinklers were required.
Mississippi University for Women will hold a candlelight vigil Wednesday to mourn the four freshmen, at 7 p.m. in the Pope Banquet Room on campus.
"This is an opportunity for the campus community to come together as one to honor these students. We want to offer our students hope and support during this very difficult time," Phillip Cockrell, director of student life at MUW, said in a statement.
Brown and McGee were studying to become nurses. Muse was majoring in theater, and Turner was studying accounting and worked in an on-campus child care center.