Cellphone video captures the arrest of 25-year-old Freddie Gray by Baltimore police on April 12, a week before he died from a spinal cord injury while in police custody (The Baltimore Sun)

The Justice Department said on Tuesday that it will conduct a civil rights investigation into how a 25-year-old man suffered a severe spinal injury while in the custody of Baltimore city police officers and later died.

The federal probe comes one day after the city’s mayor and police commissioner promised to wrap up their own investigation into Freddie Gray’s death by May 1 and allow prosecutors to decide whether criminal charges are warranted. The two investigations can run simultaneously.

Baltimore Mayor Stephanie Rawlings-Blake (D) said in a statement that she welcomes the additional scrutiny to help “get answers to the questions so many of us are still asking” about the case. “Any effort that adds additional transparency and builds community trust in this process is welcomed,” she said.

Dena W. Iverson, a spokeswoman for the Justice Department, said in a statement that federal officials have been “monitoring the developments in Baltimore” and that the department “opened this matter and is gathering information to determine whether any prosecutable civil rights violations occurred.”

Gray died in a hospital Sunday after lapsing into a coma. Police have said they are not yet sure whether Gray was injured during his arrest or while he was in the back of a police van. Officials have said the officers involved have denied using force during or after the arrest. Six city police officers have been suspended during the investigation.

Gray’s cousin, Carron Morgan, 18, said the family welcomed the federal investigations. “It should get us some answers,” he said as friends and relatives prepared for a candlelight vigil Tuesday. “The people are highly upset because of how police treat us around here and how . . . Freddie died.”

Residents in West Baltimore remained angry but calm Tuesday. Several hundred protesters took to the streets, but there were no violent incidents. A large group of protesters gathered at the Gilmor Homes, where Gray was arrested, and at the nearby Western District police station, confronting and shouting down officers.

Police, meanwhile, handed out fliers asking any witnesses to Gray’s April 12 arrest to come forward.

Some Baltimore residents and council members have complained that the police have been too slow to release information and still fell short at a news conference on Monday, when they could not explain how Gray sustained his injuries.

On Tuesday, Maryland’s two senators and three of its House members co-signed a letter to U.S. Attorney General Eric H. Holder Jr. urging him to help “to restore public confidence in the Baltimore Police Department.”

Rep. C.A. Dutch Ruppersberger (D) said that “not only does Freddie Gray’s family have a right to know the facts, so does the public.”

Rep. Elijah E. Cummings (D.), who has lived in West Baltimore for 33 years, said that the country is “at a critical moment where the public has a tremendous distrust for the police” and that an independent investigation is needed to maintain credibility.

Blind Baltimore resident Harold Perry claims to have heard Freddie Gray yelling on the night he was arrested by Baltimore police. Gray died a week after incurring a spinal injury while in police custody. (WUSA9)

Cummings said he is most angry with police officers who he believes are either remaining silent or not telling the truth. “Somebody in that group . . . knows what happened,” he said. “I do not believe they have the right to remain silent about how this gentleman was so severely injured that he died.”

Cummings said he backs the police when they urge reluctant witnesses to help solve crimes, “and now I am asking one of these police officers to come forward and tell us what happened. It’s incumbent for the police to do what they ask the public to do.”

The Justice Department also launched civil rights investigations into the fatal shooting of Michael Brown in Ferguson, Mo., and the chokehold death of Eric Garner in New York. Those cases have come to symbolize growing distrust and tension between law enforcement and African American communities.

In Brown’s case, federal authorities declined to prosecute officer Darren Wilson. They ruled the shooting justified but offered a scathing review of the police force. The Ferguson department, they said, exhibited bias practices aimed at arresting residents to generate revenue. The Justice Department’s report on Garner’s death has not yet been released.

The Justice Department already is conducting a review of the Baltimore Police Department’s practices after the mayor and police commissioner invited the federal agency in this past fall. Officials were concerned with a high number of settlements in lawsuits alleging police abuse or unjustified arrests.

Baltimore police have acknowledged that Gray suffered a severe spinal injury but have said they do not know how it happened. A cellphone video from a bystander shows officers on top of Gray and then dragging what appears to be his limp body to a van used to take detainees to holding cells.

The driver of the van made at least one stop on a 30-minute ride to a police station to put Gray in leg restraints, police officials said on Monday. Officials said Gray was angry and talking when he was first put in the van but was not breathing when it arrived at the station. Police acknowledged that Gray asked for his inhaler several times and that medical care should have been rendered sooner.

On Tuesday, police made public the names of six officers involved in the incident: Lt. Brian Rice, 41, an 18-year veteran; Sgt. Alicia White, 30, a five-year veteran; Officer William Porter, 25, a three-year veteran; Officer Garrett Miller, 26, a three-year veteran; Officer Edward Nero, 29, a three-year veteran; and Officer Caesar Goodson, 45, a 16-year veteran.

Police have identified Rice as the officer who first made eye contact with Gray and then chased him after he ran. A court document describing the chase said Gray ran when he saw police. When he was caught, police found a switchblade in his pocket, which was the basis for a criminal charge, according to the document, signed by Miller.

Henry Belsky, an attorney for Baltimore’s police union, said that information released so far “is so premature that it is doing more than stirring a pot that doesn’t need to be stirred.” He said that “contrary to popular belief, police officers are entitled to the same rights as other citizens — they are presumed innocent. I don’t think they are getting that.”