Family members of a Baltimore man whose death in police custody touched off unrest in Maryland's largest city are devastated and disappointed no one is being held accountable for his death, attorneys said Wednesday.

Billy and Hassan Murphy spoke to reporters Wednesday after the U.S. Justice Department announced it would not bring federal civil rights charges against six Baltimore police officers.

"This is a bitter pill for all of us to swallow," Hassan Murphy said. "It is the end of a chapter, and it is a sad and tragic chapter that has left a trail both in this city and in this country of hurt feelings, injury and disgust, and it is unfortunate that it has ended without anyone being held accountable for Freddie's death."

The Justice Department said in a statement that while Gray's death was "undeniably tragic," federal prosecutors did not find enough evidence to prove the officers willfully violated his civil rights, a high legal threshold.

Murphy said they asked the department for a chance to understand how investigators arrived at their decision. While Murphy said he and his father were initially skeptical, they came away "satisfied with the investigation taken by this particular group of lawyers," most of them holdovers from former President Barack Obama's administration.

"We understand the limited jurisdiction that the federal government has in cases like this, and the enhanced burden of proof that they have in deciding whether to prosecute or not," Murphy said.

The decision not to bring federal charges against the officers means none of them will be held criminally responsible for Gray's death. Three officers were acquitted in state court, and Baltimore State's Attorney Marilyn Mosby later dropped the remaining state cases.

Five officers face internal disciplinary hearings scheduled to begin Oct. 30.

The Justice Department said its career prosecutors and the FBI devoted "significant time and resources" to investigating the case.

"To the extent that the officers violated department policy in failing to seatbelt Gray, those failures suggest civil negligence rather than the high standard of deliberate indifference," the department said in a statement.

Billy Murphy told reporters that as the family's attorney he is privy to documents that he says will illustrate how some in the police department obstructed the investigation initially brought by Baltimore prosecutors.

"Because of my unique role, I have been legally made privy to documents that I believe, once they are able to be released to the public, will show without question that in several significant ways her investigation was sabotaged," he said.

Gray died in April 2015 after his neck was broken in the back of a police van. The 25-year-old was handcuffed and shackled, but he was unrestrained by a seat belt.