Freddie Gray Protest
A demonstrator holds a sign in front of the Baltimore Police Department, during a protest against the death in police custody of Freddie Gray in Baltimore, on April 23, 2015. On Saturday, more than 1,000 protesters were expected at a planned demonstration over Gray's death. Reuters/Sait Serkan Gurbuz

Baltimore protesters angry about the death of Freddie Gray, the 25-year-old African-American man who suffered a fatal injury while in police custody last week, vowed Saturday to stage their largest demonstration yet. More than 1,000 protesters are expected to attend a march from the site of his arrest to City Hall, Reuters reported. The protesters say Gray’s death exemplifies a history of police mistreatment and brutality against blacks in Baltimore and around the country.

Police Commissioner Anthony Batts said Friday that the city has braced for a major protest over the incident. Protesters have marched, blocked traffic and demonstrated at police stations throughout the week, as an ongoing police investigation into Gray’s death has been launched to piece together what happened after his arrest more than a week ago.

Protest leader DeRay McKesson, who rose to prominence following his role in Ferguson, Missouri, after the death of Michael Brown, tweeted details about the protesters plans Saturday morning.

"We're getting closer and the picture is getting sharper and sharper as we move forward," Batts said in a news conference, also acknowledging that gaps still remained.

The Baltimore demonstrations were the latest, and potentially the largest, since the deaths of unarmed black men at the hands of police in Missouri and New York City caused civil unrest and protests across the U.S. last year.

Baltimore Mayor Stephanie Rawlings-Blake has praised protest organizers for their mostly peaceful demonstrations. Unlike in Ferguson, where peaceful protests turned to rioting, arson and looting last fall, protests in Baltimore have resulted in just a handful of arrests and no major violence.

Police have said Gray and a second man fled when officers approached them in a high-crime area of Baltimore on April 12. Gray was caught and arrested for carrying a switchblade knife. He was then placed into a police van for transport to a police station, but was not buckled in at any time. That was a violation of police regulations, Batts said.

Officers also failed to give Gray medical attention, even though he requested it several times, the police commissioner said. After making at least two other stops, police removed an unresponsive Gray from the van and called an ambulance. He was taken to the hospital, where died last Sunday, police said.

A preliminary autopsy report said Gray suffered a spinal injury caused by blunt force. Baltimore Police Deputy Commissioner Kevin Davis said on Friday that the exact cause of Gray’s fatal injury was still under investigation.

Authorities said they expected to complete their investigation by May 1 and would turn the results over to state prosecutors, who planned an independent review. The U.S. Department of Justice also is conducting a separate probe of Gray's death. Six police officers involved in Gray’s arrest have been suspended with pay.

A wake for Gray is scheduled for Sunday, with his funeral on Monday, according to a Reuters report.

Leaders of the local and regional chapter NAACP, which also has its national headquarters in Baltimore, could not be reached for comment on Saturday morning.