Police officers who carried out the raid in which the reggae star Smiley Culture allegedly stabbed himself to death are unlikely to face criminal charges, disciplinary action or be officially questioned, the Guardian has learned.

The disclosure comes despite an admission by the Independent Police Complaints Commission that the operation at the singer's home in Warlingham, Surrey, on 15 March was "not satisfactory" and that the actions of at least one officer have been criticised.

In a confidential letter to the singer's family, Mike Franklin, commissioner of the IPCC, said: "The [IPCC] investigation has identified aspects of the operation which were not satisfactory, and criticisms have been made of some of the officer's actions. However, these do not meet the threshold for misconduct under the police misconduct system."

The family of Smiley Culture, whose real name was David Emmanuel, has bitterly criticised the Metropolitan police officers involved, none of whom have been suspended, and the IPCC's decision that the officers were witnesses and not suspects, meaning they cannot be compelled to submit to a formal interview.

They want to know why the four officers handcuffed 48-year-old Emmanuel after his fatal injury. An independent pathologist's report has stated that the stab wound would have "cause[d] rapid collapse and death within a few minutes".

They also question why the officer in the kitchen at the time of Emmanuel's death refused a direct request by the IPCC's lead investigator to give a formal interview.

"Even if foul play didn't happen that day, the officers should be being held responsible for being so incompetent that my dad died," said Shanice McConnachie, Emmanuel's 17-year-old daughter. "Whatever went wrong and led to my dad's death, it's the officers's fault for not doing their job properly. My dad was in their care.

"Their story just doesn't add up and until it does, I can't believe that my dad killed himself, " she added.

"My dad was under arrest and had an officer specifically allocated to his care. How could he walk around the kitchen and grab hold of a knife, without that officer seeing? And why would he? Even the police who were there admit he had been completely calm and cooperative up until that point."

"After he was stabbed, why did they police handcuff him? Our pathologist's report says he would have died almost instantly," she asked. "The police should have been focused on keeping his bleeding to a minimum and calling an ambulance. The IPCC and police don't seem to care about helping us get to the truth of what really went on."

In his letter to the family, Franklin said the IPCC cannot force the officers to be interviewed because they "have always been witnesses [and] as a witness, police officers … cannot be compelled to be interviewed about what they have seen". He added: "As they are not suspects, they will not be formally interviewed."

In the absence of further information from the officers, Franklin said the IPCC has "not found any evidence which would suggest any criminal acts were committed by any of the officers in the house". Because Emmanuel's death will be the subject of an inquest, he refused to elaborate on how this decision was made.

The four officers have given voluntary accounts of what happened, but Franklin admitted these did little to clear up the mystery. They do, however, confirm initial reports that Emmanuel, who faced drugs charges, "remained calm and compliant throughout and as [the police] were clearing up and the search had concluded, [his] demeanour suddenly changed."

Franklin has refused to give the officers' accounts to the Emmanuel family, saying the coroner "has asked that there is no disclosure at this time."

In the leaked letter, Franklin admitted there were no fingerprints on the knife found plunged into Emmanuel's chest. "Contrary to public perception, this is not unusual and can happen for many reasons," he wrote, adding that DNA matching Emmanuel's was found on the hilt.

Because the officers' actions are not classed as misconduct, the only formal disciplinary action they can now face is if the Met initiates an unsatisafactory performance procedure. The IPCC cannot direct a police force to initiate this procedure and although it can lead to dismissal, that will only happen if the officers do not improve their performance over a period of time.

The Met said the force cannot comment until after receiving the IPCC report.

If the report indicated there may have been a criminal offence committed, Franklin would send the investigation report to the Crown Prosecution Service. Given his admission in the letter that the investigation did not find any evidence of criminal acts by officers, this seems unlikely.

The family hired Dr Nat Cary, one of Britain's most eminent consultant forensic pathologists to conduct a second post-mortem on Emmanuel. His report, which has been seen by the Guardian, , concurred with the official cause of Emmanuel's death: a single stab wound to the heart. "I would expect such a stab wound to cause rapid collapse and death within a few minutes," he said.

He also acknowledged: "There is no evidence of any sharp type injuries to the hands, including no evidence of defensive type injuries against sharp weapon attack."

But he added: "In many cases with a single stab wound, no defensive type injuries are seen, including in cases with third party involvement."

Cary concluded: "Whilst it is clearly possible that the fatal stab wound was as described a self-inflicted injury, on pathological grounds alone there is nothing to determine that this was in fact the case, although it is fair to say that the site chosen is one of the sites that may be used in self-infliction."