CHOCTAW, Oklahoma - Investigators are trying to figure out what sparked a fatal fire Thursday night at an apartment complex in Choctaw.

The fire began around 10 p.m. at Mill Creek Apartments in the 14000 block of S.E. 29th Street, near Henney Road. Flames were shooting from the structure when firefighters arrived. It took crews about 45 minutes to get the fire under control.

When they entered the building, they found the victim's body.

"The fire was basically contained to one apartment, both downstairs and upstairs," said Oklahoma County Sheriff John Whetsel. "When entry was made, a body was discovered in the upper, upstairs portion of the apartment."

The victim was the sister of the person who lived at the apartment. The resident was not home at the time of the fire. The victim's name has not yet been released.

County and state investigators stayed at the scene for several hours. They say it appears the fire started downstairs, but they don't know yet what caused it.