Choi has had conversations with Hennepin County Attorney Mike Freeman, who earlier this year said grand juries would no longer be used in officer-involved shootings, but he says he needs more time to think about the best course of action.
The Ramsey County Attorney's Office has always used a grand jury in past officer-involved shootings, a spokesperson said.
"I think this is a very extraordinary case that doesn't happen on a regular basis," Choi commented at the news conference.
No matter who makes the decision, Choi says, "I assure you, we will prosecute this case to the fullest extent of the law" if charges are brought against the officer.
The Ramsey County Attorney's Office has urged the Minnesota Bureau of Criminal Apprehension to conduct a "prompt and thorough" investigation into Castile's death.
The BCA will then present its findings to the county attorney's office, but Choi said there's no timeline for when that may happen.
The Facebook video
"It will certainly be part of the evidence, without question," Choi said of the Facebook video that showed the immediate aftermath of Wednesday night's shooting.
But he cautioned people that the video only shows part of the story, and there will be other things – other facts – that will be gathered and used to complete the investigation, before it's presented to the county attorney's office.
"What is depicted [in the video] makes you sad to watch," Choi said. "But we have to have the total picture, and that's what investigators are looking at."
A call for peace
Choi called the fatal shooting "tragic and sad in so many ways," and expressed his condolences to those who knew Castile.
"I know people are angry, frustrated, devastated – and they have a right to be," Choi said, but he called for peace across the nation.
"We must do better in our state and our nation to improve police-community interactions to ensure the safety of everyone in this country," particularly African Americans, Choi remarked.
He also condemned the fatal shooting of five police officers in Dallas Thursday night, saying "there is no justification for what happened."