HEMPSTEAD, Tex. — The authorities on Monday offered new details of the final hours of the life of a Chicago-area woman who was found hanged in a jail cell in Texas three days after she was arrested during a traffic stop.

A Waller County sheriff’s official described a timeline for the jail cell of the woman, Sandra Bland, that started early in the morning of July 13, when she refused a breakfast tray around 6:30 a.m., until a jailer found her hanging shortly after 9 a.m. For about 90 minutes during that period, there was no movement by jail officials in the hallway leading to her cell, according to a video that the authorities released from a camera inside the jail.

“This investigation is still being treated just as it would be a murder investigation,” the Waller County district attorney, Elton Mathis, said. He said the case is likely to be turned over to a grand jury expected to be impaneled in August.