With protesters marching through Baltimore streets and lawmakers pleading for federal help, U.S. authorities launched a civil rights probe Tuesday into the death of a 25-year-old man whose arrest by police led to horrified screams and a broken spinal cord.

The U.S. Justice Department said it has been “monitoring” the case of Freddie Gray, who died Sunday, a week after he was arrested by Baltimore police. The death of Gray, who is black, is the latest to spark outcry and protest across the nation for perceived heavy-handed police treatment of minorities.

“Based on preliminary information, (Justice) has officially opened this matter and is gathering information to determine whether any prosecutable civil rights violation occurred,” the department said in the statement.

Members of the Maryland congressional delegation had called on Attorney General Eric Holder to take the action Tuesday.

“Freddie Gray’s family and the residents of the city of Baltimore deserve to know what happened to him while he was in police custody,” the members wrote in a letter to Holder.

“We need answers. While the vast majority of police officers act within the law to serve and protect their communities, incidents like this degrade the trust necessary to maintain the relationship between law enforcement and communities … We need the facts to restore the public confidence in the Baltimore Police Department.”

Protesters chanting “All night! All day! We’re gonna fight for Freddie Gray!” filled a Baltimore city block and police on horseback tried to quell potential unrest.

A crowd outside the Western District Police Station on Tuesday included 53-year-old Pricilla Jackson, carrying a sign reading, “Convict Freddie’s killers.”

The federal government enters the case as the city has opens its own inquiry and as six Baltimore officers have been suspended pending the outcome of the local investigation. Police reports filed earlier this week indicated that Gray, whose spinal cord was nearly severed in his neck while in custody, had been arrested “without force or incident.”

At a news conference Monday, Police Commissioner Anthony Batts said investigators are still trying to determine how Gray suffered his injury and added that he appeared to have been breathing and talking on his own when placed in a police van after being taken into custody on April 12.

Deputy Commissioner Jerry Rodriguez said he knew that “when Mr. Gray was placed inside that van he was able to talk. And when Mr. Gray was taken out of that van, he could not talk and he could not breathe.”

“I am deeply troubled by this,” Rodriguez said. “We all want to know, but I can’t answer what I don’t know.”

Police released videos showing Gray being taken into custody, but they do not capture what happened inside a van.

Rodriguez said the officers involved have been suspended and that an autopsy showed Gray suffered a spinal injury that led to his death. He said the autopsy showed no other body injuries.

“What we do not know, and need to get there, is how he suffered that injury,” Rodriguez said.

The Gray family’s lawyer, Billy Murphy, has said that Gray’s “spine was 80% severed at his neck.”

Batts said Gray asked for an inhaler initially and again several times during his transport for medical care.

“There were several times he made a medical request,” Batts said. “He asked for an inhaler, and at one or two of the stops it was noticed that he was having trouble breathing and we probably should have asked for paramedics.”

Mayor Stephanie Rawliings-Blake said Monday that she shared the community’s frustration at the lack of answers as to why Gray died while in the custody of police and said she was angered “not only that we’re here but that we don’t have all the answers.”

Video taken by a bystander does not show the injury take place, but it does show police officers dragging Gray to a police van. Gray is heard crying out in pain.

In a police report filed with the court, Officer Garrett Miller wrote that Gray was stopped after fleeing “unprovoked upon noticing police presence.” Miller said a knife was found clipped to Gray’s pants pocket and he was arrested.

“During transport to Western District via wagon transport the defendant suffered a medical emergency and was immediately transported to Shock Trauma via medic,” MIller wrote.

Police say they called emergency medical staff to care for Gray at the police station 30 minutes after the arrest. Murphy says it was far longer than that.

“His take-down and arrest without probable cause occurred under a police video camera, which taped everything including the police dragging and throwing Freddie into a police vehicle while he screamed in pain,” Murphy said.

Gray’s arrest sparked “Justice for Freddie” protests that intensified after his death.

“I take very seriously our obligation of transparency,” Rawlings-Blake said. “We also have to balance that with our obligation to ensure a proper and thorough investigation is undertaken.

“We have to move forward in a responsible way to determine all the facts of this incident so that we can provide the community with answers, real answers that they deserve.”