Top officials here acknowledged Friday that Freddie Gray was not treated properly when he was arrested nearly two weeks ago but said they are still investigating the severe spinal injury that appears to have led to his death.

Police Commissioner Anthony W. Batts said Gray was not seat-belted after being placed in a transport van, a violation of department policy. Deputy Commissioner Kevin Davis said that Gray was not offered medical attention despite several requests and that officers should have called for an ambulance when they arrested him.

Gray, 25, died Sunday, a week after he was arrested in a West Baltimore housing project. Questions about what happened to him have spurred days of protests and thrust Baltimore into the center of the debate over a spate of deaths caused by law enforcement officers.

Gov. Larry Hogan (R) and Baltimore Mayor Stephanie Rawlings-Blake (D) appealed to the public Friday to remain calm this weekend, when a large demonstration is planned.

“I know we are part of a national discussion,” Rawlings-Blake said after meeting with clergy members. “This community is intent on seeking justice for Mr. Gray.

“If you are going to come here, come to help us,” she said,

Hogan, in a statement, said: “I cannot begin to understand the level of heartbreak and pain felt by the family of Mr. Freddie Gray. My thoughts and prayers are with them and the entire Baltimore community as we grieve this tragic loss.”

The governor said he appreciated “the peaceful expressions of frustration displayed in the city. . . . It is my hope that events planned for this weekend continue to reflect positively on the community.”

Batts said more than 30 Baltimore police investigators are working to determine what happened to Gray. Batts has promised to send a report to prosecutors by Friday.

Gray appeared to be limp after he was handcuffed but was able to climb into the back of the police van on his own and could stand on one leg, Batts said. When the van driver stopped the vehicle a block later to put Gray in leg irons, the prisoner was talking and requested an inhaler for asthma. Police said the driver reported that Gray was acting irate.

The commissioner said detectives are looking into what happened when the van stopped a second time, a few blocks away at Dolphin Street and Druid Hill Avenue. Officers opened the van door, found the cuffed and shackled Gray on the floor, and put him back on the seat, Batts said.

Police were to release surveillance video later Friday showing witnesses with whom they would like to speak and photos that show some of Gray’s interaction with officers that Sunday morning.

The Maryland Coalition for Justice and Equality — which includes the ACLU of Maryland, the Maryland and local NAACP chapters and the Baptist Ministers Conference — held its own news conference Friday and called on Hogan to launch a statewide investigation of deaths and injuries in police custody.

The group also asked the governor to convene a special legislative session in Annapolis to address police issues, including a more comprehensive police body-camera bill than the one approved during the recent General Assembly session. That bill sets policies for jurisdictions where cameras are used but does not require police departments to use them.

Coalition members said Gray’s death should be a catalyst for Hogan to take executive action.

“This is not just about Freddie Gray and the city of Baltimore,” said Sara Love, the public policy director at the ACLU of Maryland. “We have a serious problem in Maryland with police-community relations.”

Hogan has asked Lt. Gov. Boyd Rutherford (R) and former state delegate Keiffer Mitchell, who is from Baltimore, to serve as his liaisons to Rawlings-Blake with regard to the investigation of Gray’s death.

The governor says he plans to sign several public safety bills Tuesday, including the existing body-camera bill and a measure that doubles the limit for civil judgments in police brutality and other claims against cities and counties from $200,000 to $400,000.

Although some activists have called on Rawlings-Blake to fire Batts, she dismissed those requests, saying the police commissioner is in the midst of reform efforts that she believes have driven down complaints of excessive force.