Two police officers present at the 2014 choking death of Eric Garner have been called to testify before a federal grand jury in Brooklyn that has begun hearing evidence, a source confirmed on Thursday.

The Justice Department has been investigating the death of Garner since a Staten Island grand jury declined to indict NYPD Officer Daniel Pantaleo on charges of using excessive force.

Garner died after Pantaleo grabbed him around the neck during an arrest for selling loose cigarettes on July 17, 2014.

Experts have been divided on whether there is a legal basis for charges that the officer intentionally violated Garner’s civil rights during the arrest.

Calling witnesses before a grand jury is a significant development, but doesn’t necessarily mean an indictment will be returned. The source said the officers testified on Wednesday.

The start of testimony before a federal grand jury was first reported Thursday by the New York Daily News.

Stuart London, Pantaleo’s lawyer, said he had not been contacted by the Justice Department and was surprised to learn a grand jury was convened.

London also said he wasn’t sure if it was a “criminal prosecution grand jury” convened to get an indictment, or an “investigatory grand jury” designed to compile evidence that might end up issuing a report urging reforms in areas such as police training.

A spokeswoman for Brooklyn U.S. Attorney Robert Capers declined to comment. Jonathan Moore, a lawyer for Garner’s family, did not immediately respond to a request for comment.