The couple were shot dead in their bungalow
Police had identified Nottingham crime boss Colin Gunn's team of six hit men weeks before two killed a couple in a revenge attack, an inquest jury heard.
John and Joan Stirland fled their home in Nottingham to Lincolnshire after being targeted when their son shot a friend of Gunn's.
A retired detective told the jury a series of revenge shootings and petrol bombings had taken place.
Gunn has since been jailed for 35 years for conspiracy to murder the couple.
A senior police officer told the inquest at Lincoln Crown Court he felt a "moral responsibility" because the deaths had happened on his watch.
The former officer, who remained anonymous, said the two men who killed the Stirlands had been named as part of Gunn's team of hit men.
The officer told the inquest he "hadn't been aware of a specific threat against the Stirlands" and could not have prevented their deaths.
He said officers had been suffering from a "conflict of resources".
He added he had been dealing with six murder inquiries at the same time, and they had been forced to run one inquiry from a snooker room.
Frantic phone calls
Mr and Mrs Stirland were found at their home in Trusthorpe having received 25 gunshot wounds between them in August 2004.
John Russell, 29, and Michael McNee, 22, were jailed for 30 and 25 years respectively over the murders, in 2006.
Coroner Karon Monaghan has asked the jury to investigate whether police corruption played any part in the deaths and if the police failed to protect the Stirlands.
Jurors are being asked to examine whether police dealt with intelligence properly and have been given a summary of intelligence reports .
Colin Gunn was jailed for a total of 35 years
Before the couple fled Nottingham, shots were fired into their home.
Mrs Stirland's son, Michael O'Brien, is being allowed to watch the proceedings in jail, where he is serving a life sentence for the murder of Marvyn Bradshaw, 22, outside a pub in Bulwell, Nottinghamshire.
The inquest heard senior police officers knew Gunn's organisation, which numbered between 30 and 40, planned to seek revenge against O'Brien.
But detectives did not know of the crime boss's plans to target his mother, a 51-year-old nurse, and his 55-year-old stepfather.