Baltimore police have opened a criminal investigation into the death of a man who died Sunday, apparently as a result of injuries sustained in police custody, the Associated Press reported. Freddie Gray, 25, of Baltimore was arrested last week by Baltimore police.

Police said uniformed bicycle officers attempted to stop Gray, but he fled on foot. “The officers caught him and restrained him on the ground while awaiting backup,” the Baltimore Sun reported. The police have not said why Gray was arrested. 

Gray’s family said he sustained serious injuries during or after the arrest. Family attorney Billy Murphy described the extent of Gray’s injuries at a press conference Sunday.  

"His spine was 80 percent severed at his neck,” Murphy said. “He lapsed into a coma, died, was resuscitated, stayed in a coma and on Monday, underwent extensive surgery at Shock Trauma to save his life. He clung to life for seven days and died today [Sunday] at approximately 7 a.m."

Video recorded by a civilian of the arrest shows Gray being arrested and placed into the back of a police van, but the video does not capture the full encounter. Police have yet to release any official reports or documents regarding the arrest.

"The individual attempted to flee and was able to run as we attempted to make a detention of him," Baltimore Deputy Police Commissioner Jerry Rodriguez told Sunday's press conference. "This individual was not able to run when he was transported by ambulance to the hospital. That's what we're trying to investigate: What exactly happened. What actions or inactions may have contributed to this."

Officials say once Gray was transported in the van to the police station, an ambulance was called and brought him to the University of Maryland R. Adams Cowley Shock Trauma Center. 

Since Gray’s arrest, protesters in Baltimore have mobilized. The Justice League NYC held a demonstration outside the police station where Gray was booked Saturday, and protesters assembled Sunday at the site of his arrest. 

Baltimore Mayor Stephanie Rawlings-Blake promised she would hold "the right people accountable."

Richard Shipley, Gray's stepfather, told the Baltimore Sun: "He's gone. What else is there to say?"