Donte Allen, 22, was next to Gray after he too was arrested on April 12 - but was kept in a separate part of the vehicle and separated from his fellow prisoner by a solid partition.
He also claimed police were aware of how severe Gray's injuries were by the time they arrived at the police station - and even claimed he had no pulse when they arrived.
Ultimately, Gray lived for a week after the injured, but was declared dead in hospital on April 19.
Allen, who was arrested for an unspecified but minor offense, spoke out about his time next to Gray in an interview with local news station WBALTV.
It came alongside claims that police confusion led to the wrong type of medical help being sent for Gray, leading to paramedics only arriving with the resources to treat a broken arm.
Describing the journey with Gray, Allen said said: 'When I got in the van, I didn't hear nothing. It was a smooth ride. We went straight to the police station.
'All I heard was a little banging for about four seconds. I just heard little banging, just little banging.'
Gray was in the van for 45 minutes, and Allen is thought to have been picked up towards the end of the journey.
According to a medical report seen today by local news reporters, he was standing, bent over and handcuffed, inside the vehicle - and at some point suddenly fell forward and hit his head on the inside of the van.
That report contradicts suspicions that Gray could have been injured by officers during his arrest.
Allen's earlier account of the ride was also the basis for a police affidavit, which explosively claimed that Gray may have caused the catastrophic neck injuries to himself by slamming his own body against the van.
The report was leaked to the Washington Post, and is apparently based on Allen's testimony even though that document cites a '38-year-old man' captive in the van.
Allen seemed to downplay that theory in his latest interview, saying that he heard 'a little banging' lasting around four seconds.
He rapped with his knuckles on a nearby railing to illustrate the comparison.
The events inside the van - which still remain mysterious - have caused riots and unrest in Baltimore, and a heavy police presence and a city-wide curfew have been imposed in a desperate bid to maintain order.
Further accusations emerged against the police today, as a separate report by WBLATV claimed that medical records showed paramedics were only sent out expecting to treat a broken arm.
The station claimed the result was insufficient resources being devoted to the call, and vital time being wasted, which could have exacerbated Gray's condition.
Baltimore Police have been investigating the incident internally, and today handed over their report to local prosecutors.
Baltimore Police Commissioner Anthony Batts said that a team of investigators had carried out an urgent examination of events.
The development means it is now up to prosecutors to decide if anyone will be charged in connection to Gray's death.
Gray died with 80 per cent of his spine severed at the neck, lawyers for his family say, portraying him as the latest young African American to die at the hands of the police.
Police, meanwhile, released a tally of Baltimore police officers injured since riots erupted Monday, putting the total at 98, 43 of whom required emergency medical treatment.
Meanwhile in New York, police said 143 people were arrested during related protests there on Wednesday night.
Protesters gathered in Manhattan's Union Square on Wednesday, following calls on social media to demonstrate in solidarity with Baltimore, the site of daily demonstrations since Gray's death on April 19.
Rallies also took place in Boston and the US capital Washington on Wednesday, as simmering anger over alleged police brutality and discrimination against blacks again bubble to the surface.
Baltimore protests first turned violent Monday, and officials there have called for calm in the wake of the unrest, imposing a 10:00pm-5:00am curfew, which remains in place.
Freddie Gray was a 25-year-old African-American who grew up in Baltimore's impoverished west side
Nicknamed 'Pepper', he was described by an ex-girlfriend as happy-go-lucky with an infectious sense of humor.
The Baltimore police knew him, however, as a 5ft-8ins felon who had notched up at least 18 arrests and a handful of convictions - mainly for Class A drugs but also burglary, assault and illegal gambling.
He was said to have set off running at the sight of police patrolling a well known open-air drug market.
He was taken into custody for possession of a switchblade and during transport to the station he experienced what officers described as 'a medical emergency'.
Gray, who had asthma, requested an inhaler and had trouble breathing in the van, but police didn't provide his inhaler.
According to Gray's family his spine was severed 80 per cent at his neck, three vertebrae were fractured and his larynx was injured.
Court papers describe Gray's childhood as problematic. He lived with his heroin-addicted disabled mother in a home in Sandtown-Winchester that contained enough poisonous lead in the peeling painted walls and windowsills for a court settlement to conclude that he and his two sisters were incapable of leading normal functioning lives.
Lab tests conducted in the 1990s showed that they had levels of lead in their blood nearly
double what the state of Maryland defines as the minimum for lead poisoning.
In Baltimore, more than 2,600 children have been found to have high levels of lead in their blood, according an annual report released by the Maryland Department of the Environment in 2014.
'This is the toxic legacy of lead-based paint,” Ruth Ann Norton, head of the Green & Healthy Homes Initiative and a founding member of the Maryland Lead Poisoning Prevention Commission, told the Baltimore Sun.
'Our kids are ill equipped to stay in the classroom, finish school. They’re very unlikely to go on to higher education. They’re less likely to be able to hold a job', she said.
'They’re less equipped to be able to overcome the poverty and other circumstances that pull them down. Children with lead poisoning will have defects, regardless of whether their parents are ‘nice’ or not.'
Gray lived off the resulting 'lead check' settlement although it is unclear exactly how much he received.
Whatever money he did have he was said to spend buying designer accessories.
The Sandtown neighborhood is a 72-block neighborhood made up of almost entirely of African Americans.
More than one-third of residents live below the poverty line, and nearly a quarter are unemployed.
The majority of Maryland's state prison population are said to said to hail from Sandtown, according to the Justice Policy Institute.