Guyger said she realized she was in the wrong apartment when she flipped on the light switch.
Jean's relatives joined the district attorney for the announcement of the charge.
"He didn't deserve it, he was seated in his own apartment".
Asked why the grand jury indicted Guyger on a murder charge, Johnson said, "We presented the evidence and explained the law". On the day of the shooting, Guyger's unit had arrested multiple suspects for armed robbery, he said.
Although Johnson said she is prohibited from discussing what evidence the grand jury reviewed, she did say her office conducted more than 300 interviews and ordered forensic testing on a number of items. Dallas County DA Faith Johnson commented on the change of the original manslaughter charges.
"The Jean family's loss can not be restored to them, but we will continue to work to ensure that police officers are held to the same standards as everyone else in the Dallas community and across the state of Texas", she said. "She fired a gun in the direction of a person she knew was standing in front of her".
This Sept. 21, 2017, file photo provided by Harding University in Search, Ark., shows Botham Jean leading worship at a university presidential reception in Dallas.
Jean's family says in the suit that Guyger had a history of violence and used excessive force against Jean that fateful night in September, resulting in his wrongful death.
Jean's death ignited outrage in Dallas and around the country as questions about Guyger's version of events piled up and officials didn't take her into custody for days after the shooting.
Guyger turned herself in to authorities Friday afternoon. The officer was arrested and booked into jail in neighboring Kaufman County before being released on bond. "I look forward to the next test, which is a conviction ... a proper penalty so she can reflect on what she has done".
Guyger was initially charged with manslaughter, which is punishable up to 20 years of prison.
The grand jury upgraded the charge to murder.
Family attorney S. Lee Merritt said the grand jury decision is "groundbreaking, but it is also just a start". She was sacked weeks later by the Dallas Police Department.
Mr Jean's killing thrust Dallas into the national conversation on the intersection of race and law enforcement, a dialogue revived by the high-profile trials of officers charged with murder in police shootings. And then there's the element of race: "Guyger is white; Jean was black".