PUEBLO, Colo. -- Federal agents from the US Bureau of Alcohol, Tobacco and Firearms are expected to arrive in Pueblo to assist local authorities in determining what caused an explosion which killed one person and demolished the Branch Inn on Thursday afternoon.

On Friday, search dogs went through the debris left by the blast to make sure there were no other victims. Also fire crews and engineers checked the structural integrity and any hazards the buildings might pose to the public. Two of the buildings left standing were determined to be unsafe and remain closed.

Pueblo Fire Department has narrowed the possible causes of the ignition to either a natural gas leak or an intentionally-set detonation. While no evidence points directly at the latter, authorities said they can’t rule out the possibility.

Authorities have named the victim of the blast as 22-year-old Ashley Johnson of Pueblo. Johnson was in a boutique next door to the Branch Inn. She was trapped in the debris for 90 minutes before crews were able to extricate her. She later succumbed to her injuries.

Police have confirmed several other victims who were injured in the explosion. Eugene Roney, 74, Kevin Trujillo, 40, Jennifer Flower, 23, Nick Stabile, 18 and Frank Vigil, 41 – one of the owners of the Branch Inn - are all recovering from injuries which are not believed to be life-threatening.

The intersection of Union Avenue and C Street, where the restaurant is located, remains closed to all traffic while the investigation continues.