UPDATED: April 22, 2015 5:11 p.m.

BALTIMORE — Amid tears and cries for justice, demonstrators poured into the streets of Baltimore carrying signs emblazoned with the name of a man who died from a spinal injury he suffered while in police custody.

Tuesday’s demonstration marked the beginning of a week of protests and rallies planned across the city.

The Justice Department said earlier in the day that it has opened a civil rights investigation into the death of Freddie Gray, a 25-year-old black man who suffered a fatal spinal-cord injury under mysterious circumstances after he was handcuffed and put in the back of a police van.

At the site of Gray’s arrest, more than a thousand demonstrators gathered to remember Gray, who friends and relatives say was kind, funny and generous, and call for police reform.

“I want this to be a sign to the Baltimore Police Department that this is not an act of surrender,” said Pastor Jamal Bryant of the Empowerment Temple, one of the rally’s organizers, as he called on those in the crowd to raise their hands. “It’s a sign of strength, of one unity and one commitment that we will not rest until we get justice for Freddie Gray.

“The world is watching,” Bryant said. “The world is watching, and the world needs to see that black Baltimore is unified.”

Gray was taken into custody April 12 after police “made eye contact” with him and another man in an area known for drug activity, police said, and both men started running. Gray was handcuffed and put in a transport van. At some point during his roughly 30-minute ride, the van was stopped and Gray’s legs were shackled when an officer felt he was becoming “irate,” police said.

Police Commissioner Anthony Batts said Gray asked for an inhaler and then several times asked for medical care. He was eventually rushed to a hospital.

Gray died Sunday — a week after his arrest — of what police described as “a significant spinal injury.”

Exactly how he was injured and what happened in the van is still not known.

Demonstrators called for answers, accountability and a change to how they say people in inner-city Baltimore are treated by officers patrolling the neighborhood.

Pricilla Jackson carried a sign reading, “Convict Freddie’s killers,” that listed the names of the six officers suspended with pay while local and federal authorities investigate the death. Jackson, who is black, said she wants Mayor Stephanie Rawlings-Blake to know that she and others have been brutalized by police.

“They’re hurting us when they throw us to the ground and kick us and punch us,” said Jackson, 53.

As night began to fall, the crowd gathered outside of the Western District station house and held candles in front of banners that read, “Black Lives Matter, Stop Police Terror.”

“How many of you have a Freddie Gray in your family?” shouted one demonstrator at a line of police officers outside of the station. “How many of you have lost a child, a brother?”

Another demonstration is planned for Wednesday evening at the site of Gray’s arrest, and on Thursday protesters are expected to gather outside City Hall.

Baltimore Police said Wednesday that five of the six officers provided a statement to investigators. The investigation will be turned over to the State’s Attorney’s Office.

Official say the second person who was inside the prisoner transport wagon with Gray is a witness in a criminal investigation. His name will not be released.

RELATED: Police: Video Didn’t Capture Suspect’s Fatal Spine Injury

Dr. Ali Byden, a neurosurgeon at Johns Hopkins Hospital, says it would take extreme force to inflict the kind of spinal injury Freddie Gray suffered, WNEW’s Karen Adams reports.

The spinal cord is the extension of the brain, and vertebrae protects the spinal cord.

“You have to exert a significant amount of force on the spine, on the neck in order to injure the underlying spinal cord,” Byden says. A car crash, diving into shallow water, and smashing your head against a hard surface can all cause severe spinal injury, he adds.

RELATED: Man Injured During Arrest by Baltimore Police Dies

Baltimore police have said they’re looking into why Gray was stopped and what led to his injury.

In federal civil rights cases such as this one, investigators look for evidence that an officer willfully violated a person’s civil rights by using unreasonable force.

Justice Department spokeswoman Dena Iverson said investigators are “gathering information to determine whether any prosecutable civil rights violation occurred.”

It’s not uncommon for federal investigators to look into allegations of excessive police force. Justice Department investigations in the last year include probes into the fatal shooting of an unarmed black 18-year-old in Ferguson, Missouri — a case that resulted in no charges against the officer — and an ongoing review of a police chokehold death of a New York City man.

There’s a high threshold for bringing federal civil rights charges against police officers in such cases. Federal investigators must show an officer willfully deprived a person of his or her civil rights by using more force than the law allows, a standard that’s challenging in rapidly unfolding confrontations in which snap judgments are made.

Baltimore Mayor Stephanie Rawlings-Blake released the following statement on the Department of Justice’s investigation:

“From the outset of our investigation, I have repeatedly affirmed my support for an outside review into the death of Mr Gray. Whenever a police force conducts an internal investigation, there are always appropriate questions of transparency and impartiality. My goal has always been to get answers to the questions so many of us are still asking with regards to Mr. Gray’s death. Any effort that adds additional transparency and builds community trust in this process is welcomed. This outside review will assist us in getting to the bottom of what happened to Mr. Gray in the most objective and transparent way possible.”

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