HEMPSTEAD, Texas — A Texas prosecutor says there are many unanswered questions about the death of a black woman whose family disputes authorities’ finding that she hanged herself in a jail cell three days after a confrontational traffic stop, and that the case is being examined as thoroughly as a murder investigation.

Waller County District Attorney Elton Mathis said at a news conference Monday that a Texas Rangers investigation the death of Sandra Bland is being supervised by the FBI. Authorities have said the 28-year-old woman from Naperville, Illinois, hanged herself with a plastic garbage bag July 13.

Her death at the Waller County jail, about 60 miles northwest of Houston, comes amid increased national scrutiny of police after a series of high-profile cases in which blacks have been killed by officers.

“It is very much too early to make any kind of determination that this was a suicide or a murder because the investigations are not complete,” Mathis said.

He said he’s asked the Texas Rangers to do extensive scientific testing for fingerprints, DNA and to use any other valid investigative techniques “so we can figure out and say with certainty what happened in that cell.”

“This investigation is still being treated just as it would be in a murder investigation. There are many questions being raised in Waller County, across the country and the world about this case. It needs a thorough review,” Mathis said, noting, “It will go to a grand jury.”

Capt. Brian Cantrell, head of the sheriff’s department criminal investigation division, said at the same press conference that Bland’s death “was a tragic incident, not one of criminal intent or a criminal act” but that he welcomed the investigation.