Lincoln, Neb. ? Investigators Saturday were still trying to find out what caused a fire at a college fraternity house that killed one student and sent three others to a hospital in critical condition.

“The investigation went well into the night and wasn’t completed yet,” said Patrick Borer, deputy chief of Lincoln Fire and Rescue. State and local fire experts were expected on the scene Saturday, he said, but he doesn’t expect that any statements will be issued until Monday.

Borer would not say whether there were any early indications about what caused the fire or whether any activities by residents were involved.

There were unconfirmed reports from neighbors about fireworks, but Borer said he had no information.

The early-morning fire at the Phi Kappa Tau fraternity house at Nebraska Wesleyan University killed 19-year-old Ryan Stewart, of Ord, Neb., officials said. Three other students – David Spittler, 20, of Elkhorn; Travis Mann, 22, of Beatrice; and Aaron McGuire, 20, of Sioux Falls, S.D. – were sent to St. Elizabeth Regional Medical Center. They remained there in critical condition on Saturday, spokeswoman Jan Yaussi said.

The fraternity house did not have a sprinkler system, which interim Lincoln Fire Chief Dan Wright said could have reduced the severity of the fire.

Nebraska and Lincoln fire codes require all new campus dormitories and fraternity and sorority houses to include sprinkler systems, said Lincoln Fire Inspector Rick Campos. But sprinklers don’t have to be installed on older buildings unless they are being remodeled, Campos said.

The Phi Kappa Tau house was built in 1928 and is on the National Historic Register.

Officials plan to move the Phi Kappa Tau members into a vacant section of the Alpha Gamma Delta sorority house on the campus until the fraternity house is habitable, a university spokeswoman said.

Nebraska Wesleyan is a Methodist Church-affiliated liberal arts college founded in 1887. There are 1,800 students enrolled there, according to the university’s Web site.