The investigation into the death of Mark Duggan has found no forensic evidence that he was carrying a gun when he was shot dead by police on 4 August, the Guardian has learned.

A gun collected by Duggan earlier in the day was recovered 10 to 14 feet away, on the other side of a low fence from his body. He was killed outside the vehicle he was travelling in, after a police marksman fired twice.

The new details raise questions about the official version of events. The shooting triggered some of the worst riots in modern British history, which began in Tottenham, north London, in response to the treatment of the Duggan family. The investigation into Duggan's death is being carried out by the Independent Police Complaints Commission (IPCC), but the Guardian has learned new details of the shooting, and a much more complex picture than first revealed is emerging.

On the day Duggan was shot, there is overwhelming evidence he had obtained a firearm, and there is video supporting that. But the investigation is considering whether Duggan had a weapon in his possession when he was shot dead by the police.

The revelations raise questions for the Metropolitan police about the intelligence they had and its interpretation, the planning of the operation, tactics deployed, and the actions of its firearms officers.

The Crown Prosecution Service may have to consider if any officer should face criminal charges.

But the revelations also raise questions for the IPCC, whose public statements appeared to give a different impression of the shooting.

The IPCC had to correct the initial information it released, which came from the Met but which it adopted, saying Duggan had fired and that a bullet had lodged in a radio worn by a police officer. The IPCC later admitted the bullet was in fact most likely a ricochet from one fired by a police officer.

The day he was shot, Duggan hired a people carrier from a taxi firm. Officers from the Met's Operation Trident, which investigates gun crime within the African-Caribbean community, followed it.

Their intelligence that Duggan would obtain a firearm proved correct. A box, believed to have contained the weapon at some point, was found inside and at the back of the Toyota Estima people carrier.

Duggan was followed from an address in Hackney and one in Leyton, east London. As he entered Tottenham, police decided they would halt his vehicle and, fearing he had a weapon, decided to involve armed officers from their elite firearms unit, C019.

The new findings include:

• The weapon Duggan obtained was in a shoe box, in a sock, with a small hole cut away for the barrel.

• The weapon was a converted BBM "Bruni" self-loading pistol. It contained one bullet.

• Neither Duggan's DNA nor fingerprints have yet been recovered from the sock or the weapon. His fingerprints have been found on the shoe box, which was found in the back of the hired vehicle.

• Evidence suggests Duggan's weapon was not fired.

• Duggan appears to have known police were not just following him, but were going to stop him. At 6.05pm, some nine minutes before police say they shot him dead, he sent a BlackBerry message: "Trident have jammed me," he wrote, adding that people should look out for a maroon people carrier in which he believed officers from Trident were travelling.

• Toxicology tests indicate Duggan had some illegal drugs, namely ecstasy, in his blood stream. The effect on his behaviour, if any, is unclear.

• The vehicle was moved by police after the shooting, before independent investigators examined the scene.

Police following Duggan were from Operation Trident and believed the situation developing was "a crime in action", and were aware a relative of Duggan had been killed recently and that he might seek revenge for that.

A rival scenario detailed by a community source is that Duggan was obtaining a firearm after being attacked himself just days before.

Recent police shooting cases have shown that even where the person killed had no weapon, or it was some distance away, if officers can show they had a reasonable belief their life or that of others was in danger, they are highly likely to have a lawful defence.

Part of the reason the IPCC was set up was to have greater credibility within communities affected by police actions. But after the Duggan shooting, the dead man's relatives were critical of how they had been treated. The IPCC and police blamed each other for a failure to keep the family properly informed.

An IPCC spokesperson said: "The ongoing IPCC investigation into the death of Mark Duggan is examining a range of issues. We are providing updates and, where possible, answers to the family of Mr Duggan.

"This is a complex investigation that involves gathering information including witness statements, pathology, forensics and ballistics analysis and we have stated to the coroner that it will be completed within four to six months. We are unable to put information in the public domain until appropriate to do so. Ultimately, the evidence from our investigation will, rightly, be tested and challenged in a public forum before an inquest jury. We would urge people not to rush to judgment until they see and hear the evidence themselves."

In other high profile incidents involving death after police conduct, the first official version has proved wrong, adding to the damage and suspicion surrounding police actions.

Police insiders stress that firearms officers have a highly dangerous job, the risks and realities of which are little understood outside law enforcement circles.

In another development, it emerged police are under investigation over the weapon found where Duggan was shot, after it emerged it may have been used a week earlier in an assault by another person. The IPCC said tests suggested the gun may have been carried by another man in an assault, before somehow being transferred to Duggan.

The IPCC also announced that two Metropolitan police officers are under investigation over whether the assault was investigated properly. It was reported to police and no arrests were made immediately afterwards.

Sarah Green, commissioner of the IPCC, said: "Our investigation will consider whether all investigative lines were promptly identified and acted upon by officers from the Metropolitan police service and to what extent, if any, the conduct of this investigation may have impacted on the supply of the firearm found at the scene of the shooting of Mark Duggan."

In a statement the Met said: "Due to concerns about the quality of the investigative response the MPS has voluntarily referred the investigation to the Independent Police Complaints Commission.

• The headline and standfirst on this article were amended on 18 November 2011 and again on 19 November following complaints by the IPCC and the Metropolitan police that both were misleading. The Guardian has apologised for the misleading nature of the headline and standfirst and the length of time it took to recognise the serious error. See Open Door