Relatives, activists and even Baltimore city officials have more questions than answers about what happened to Freddie Gray, a 25-year-old man who died one week after he was rushed to the hospital with spinal injuries following an encounter with four Baltimore police officers.

Gray, who died Sunday morning at a University of Maryland trauma center, was stopped by Baltimore police officers on bike patrol April 12. Police have said Gray was running away from the officers when he was arrested and placed in a transport van. About 30 minutes later, Gray was rushed to the hospital in critical condition, according to police.

Billy Murphy, an attorney for Gray's family, said Sunday that 80 percent of the man's spinal cord had been severed near his neck.

Mayor Stephanie Rawlings-Blake and top police officials promised accountability and transparency Sunday at a news conference at City Hall.

"How was Mr. Gray injured? Were the proper protocols and procedures actually followed? What are the next steps to take from here?" Rawlings-Blake said.

She promised a thorough investigation and "real answers" for the community.

"I will ensure we will hold the right people accountable," Rawlings-Blake said.

Gray's family has declined, so far, to interact with police, said Police Commissioner Anthony Batts. He said the department would try again this week to share information with them.

"A mother has lost her son," Batts said. "Freddie Gray passed. My greatest hope and wish and desire is that any time we have an interaction as a police department or a contact, that everyone goes home safe."

Batts said he is assembling a "hybrid task force" that will include homicide investigators and the force investigation team.

Officers and other witnesses have been interviewed, according to Deputy Commissioner Jerry Rodriguez. However, not everyone has been interviewed, Rodriguez noted, saying the officers who are subjects of the criminal investigation have a right not to potentially incriminate themselves.

But Murphy said he has interviewed 11 witnesses as part of an investigation on behalf of the Gray family, and has asked the department for video footage, which it has declined to release to the public. Murphy said he disputes the department's timeline of events, and believes Gray was in police custody for longer than they say.

"We are tired of the words. We want to see action," Murphy said Sunday. "We want to see fair compensation for victims of police brutality, we want to see a fair response and an impartial investigation not cops investigating themselves.

"We have no confidence that the city or the police department is going to fairly and objectively investigate this case," Murphy added. "We have no confidence the investigation will reveal the truth."

Meanwhile, Baltimore's activist community on Sunday called for increased transparency and accountability of the city's police department, which last year volunteered for a Justice Department review of its policies and procedures.

Outside of the Western District station house, where Gray was brought after his arrest and before officers called for medical assistance, Cortly "C.D." Witherspoon, president of the Baltimore chapter of the Southern Christian Leadership Conference, called Baltimore a "police state" where criminalization of African American men is a pervasive problem. Witherspoon called for action, and an independent investigation into Gray's death.

"They want the citizenry to be patient. They want the citizenry to let the investigation play out," Witherspoon said. "We can't do that. There has never been honest and genuine conversation with the police department and the people on the ground. We want an independent investigation. We want the officers fired, we want them stripped of their pension and we want them charged."