BALTIMORE (AP) -- Authorities' refusal to provide more than a few sketchy details about the Freddie Gray investigation is fueling suspicion and mistrust as a weekend of protest rallies looms.

A protester watches as police enforce curfew for the third night. (AP Photo/Patrick Semansky)

The secrecy may be legally appropriate, but many in Baltimore were finding it hard to be patient Thursday when police revealed next to nothing about the criminal investigation they turned over to the state's attorney's office.

Nearly two weeks after Gray's death, the public still doesn't know much more than it did on Day One. The central question - what caused his fatal spinal cord injury while he was in police custody earlier this month - remains a mystery.

"The transparency is just not there," the Rev. Cortly "C.D." Witherspoon said after Police Commissioner Anthony Batts refused to answer any questions Thursday.

Batts said a 10 p.m. curfew for all residents and a state of emergency declared by Maryland Gov. Larry Hogan would remain in effect through Sunday. The curfew went into effect for the third night Thursday with no major incidents.

"We have two very large marches that are going to take place on the weekend," Batts told a news conference Thursday evening. "We have a lot more that are popping up by the minute."

Protesters were planning large demonstrations in Baltimore and around the country Friday, which is May Day, a date traditionally used to champion labor issues but which has expanded over the years to include such causes as women's and immigrant rights. This year, many planned to add civil rights and the slogan "black and brown lives matter."

Friday also was the day protesters initially expected police to release information about their investigation. Batts said the report was delivered a day ahead of time to State's Attorney Marilyn Mosby, and that from now on, any questions should go to her.

Mosby released no information; instead she issued a statement asking "for the public to remain patient and peaceful and to trust the process of the justice system."

Acting Attorney General John Hoffman addresses New Jersey State Police troopers in Baltimore (NJ State Police)

A coalition of news media organizations, including The Associated Press, sent a letter Thursday evening to the Baltimore Police Department seeking the immediate release of the report as information that would serve the public interest.

With rumors flying about how Gray's spine was "80 percent severed," as his family's lawyer Billy Murphy put it, police did release a new piece of information Thursday, but it served mostly to raise more questions about how truthful the six suspended officers have been with investigators.

Deputy Commissioner Kevin Davis said investigators discovered a security camera recording showing that the police van carrying Gray had made a previously undisclosed, second stop, after the 25-year-old black man was put in leg irons and before the van driver made a third stop and called for help to check on his condition. The van then made a fourth stop, to pick up another passenger, before Gray arrived at the police station with the fatal spinal-cord injury that left him unresponsive.

Grocery store owner Jung Hyun Hwang told The Associated Press that officers made a copy last week of the video from his store. He said the only other copy was stolen, along with his video equipment, by looters Monday night. He said he didn't see the recording.

Police have said Gray was obviously injured and asking for medical help when he was hoisted into the van on April 12 and unresponsive on arrival at the station. He died in a hospital after a week in a coma.

Beyond the slim chronology, authorities have refused to discuss the details of Gray's handling or statements from any of the six suspended officers. Their names are known only because the AP and other news organizations obtained the documents police filed charging Gray with carrying a switchblade.

Bruce Goldfarb, a spokesman for the Maryland State Medical Examiner's Office, told the AP Thursday that Gray's autopsy is complete, but the forensic investigation is still in process and no conclusions have been sent to police or prosecutors.

Legal experts and the Gray family lawyers say secrecy is appropriate at this point in the probe, when it's still possible that some witnesses haven't been questioned, or even found.

A police officer watches as a man runs down North Avenue as a curfew approaches in Baltimore (AP Photo/Patrick Semansky)

"By releasing too many details, you run the risk that witnesses' testimony will change to mirror the details you have released," said David S. Weinstein, a former federal prosecutor now in private practice in Miami. He said investigators must verify or corroborate much of the information they receive, and meanwhile the public could be misled that the probe is leading to a particular outcome.

Investigators also face challenges with police that are different from killings by civilians. There's the question of whether an officer acted "reasonably" considering the circumstances - a common defense in use-of-force cases.

Meanwhile, protests over Gray's death are spreading and continuing. Crowds gathered Thursday in Philadelphia and Baltimore. Other protests led to arrests in New York and elsewhere.

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