New York: The city of Baltimore is on edge as it awaits the findings of a police investigation into the death of Freddie Gray, the young black man who sustained a fatal spinal injury in a police van. His death has sparked massive protests throughout the United States.

New evidence about Gray's final hours was revealed on Thursday as police completed their investigation, with the police commissioner admitting the van had made an additional stop - four in total - during the journey. The stop had not been disclosed previously and was only discovered in private camera footage obtained during the investigation.

A local TV station also reported the medical examiner had concluded Gray, who was not wearing a seatbelt as required, died after his head was slammed into the back of the police van, though how that happened was not clear. Courts have previously ordered major payouts for people who sustained serious injuries during "rough rides" in Baltimore Police vehicles, where vans are driven in a manner to cause injury to unbuckled suspects, according to the Baltimore Sun.

Police concluded their investigation a day early on Thursday and handed the report to the state's attorney, as anger towards police simmered and protests spread around the country. Protesters were calling for the investigation's findings to be made public as soon as possible but there was cynicism about whether any police officers would be indicted regardless of the findings.

On the streets of Baltimore the atmosphere was grim. Police lined the streets around the burnt out stores of Pennsylvania Avenue, which saw some of the worst of Monday night's violence.

Asked how he expected the coming days would be one officer said simply, "horrible," and then for emphasis he said it again, stringing out the word, "horr-i-ble." He said he had been told to expect to be working around the clock. He had already sustained injuries to his leg from a brick thrown on Monday.

The city's tourist and central business looked as though they were under occupation, with National Guard troops carrying assault rifles lining some of the major streets. A peaceful march into the city centre took place in the late afternoon, and an emergency curfew remains in place.

Almost 150 people were arrested in New York City on Wednesday night, one of many protests around the US this week. The rally began with at Union Square, where Danette Chavis, a mother who blames the NYPD for the death of her son in 2004, said police were allowed to kill with "impunity".

"We have seen police go roughshod in Ferguson, in Oakland, most recently in Baltimore... there's no reason why parents like myself, or the victims, should have to be made to march and beg and protest for justice," she said.

Protesters have also marched in Philadelphia, Washington, Seattle and Ferguson, where Michael Brown, a young black man, was shot by a police officer last year.

More than 200 people were arrested in Baltimore during the most serious unrest on Monday in which numerous buildings were burned and looted. One hundred people arrested that night were released without charge late on Wednesday after the public defender's office filed habeas corpus petitions demanding their release. Conditions in the booking cells were reportedly poor and crowded, with no beds, blankets or pillows, with up to 15 women sharing a cell and sleeping on the floor, according to one lawyer.

Paul DeWolfe, the Maryland Public Defender, told Fairfax Media bail for those who had been charged had been set at excessive levels, with reports of bails of up to $US100,000 ($126,000) - well out of reach for residents in the impoverished neighbourhoods where the riots took place.

"Putting excessive bail on people who can't afford it, I think it's a discriminatory practice," he said. "If you have money... you pay the bond and get out. If you don't have resources... then you're treated differently."

Since Monday's riot, 98 police officers in Baltimore have been injured in the unrest, with 43 requiring  hospitalisation.

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