A special grand jury will weigh possible criminal charges against an NYPD sergeant who fatally shot a 66-year-old bat-wielding woman, the Bronx district attorney said Monday.

“It is important to determine exactly what happened in this tragic incident,” DA Darcel Clark said in a statement.

Clark said she was going to ask the courts “to impanel a special grand jury’’ to hear the case against Sgt. Hugh Barry.

A law-enforcement source said the decision to take the case to a grand jury wasn’t easy.

“There was a genuine debate over the best course of action,’’ the source said.

“Some people in the bureau are saying that the grand jury is the most appropriate venue to present all the evidence for determination of whether or not to bring criminal charges.

“The other school of thought believes it’s the office trying to project to the community that we are treating it seriously and trying to mitigate damage to community relations in a case the office believes it doesn’t have much chance [to win] at trial.”

Barry shot schizophrenic Deborah Danner in her apartment Oct. 18 after she grabbed a bat and rushed him, authorities have said.

Barry’s union has said he feared for his life.

Additional reporting by Emily Saul