"It is a form of execution," said Richard Latham QC, prosecuting at St Alban's Crown Court. "The colonel was lying on his back in the hall passageway, the door was wide open and his foot was hanging over the threshold."
Docherty-Puncheon has already been convicted of the murder of Fred Moss, a 21-year-old traveller, later the same year, in November 2004.
Mr Latham told the jury: "He is a man capable of cold blooded murder. One can imagine a number of people killing in a temper. It takes a particular person to kill in cold blood and the allegation is that that is precisely what the killing of Fred Moss was and indeed what the killing of the colonel was."
Paramedics initially thought that Lt Col Workman had died of natural causes but the undertakers found blood and a lead pellet when they started to move his body.
A post mortem examination showed he had been killed with a single shot from a sawn-off shotgun at a range of 11 to 13ft. Neighbours claimed to have heard a blast at about 8.15pm but did not see or hear anyone drive away.
Mr Latham said: "You may think the killer must have knocked on the door and as Col Workman went to the door and opened it in all probability he was taken totally by surprise." Docherty-Puncheon was living a 40-minute walk away in Stocking Pelham when the killing took place and had regularly been shooting despite not having a shotgun certificate since 1997.
Some time before the killings his uncle, Peter Ward, a farmer, had seen a sawn-off shotgun in his car, Mr Latham said.
Docherty-Puncheon was arrested the morning after the colonel's death and claimed he did not know who the dead man was. But he later admitted having worked for the colonel as a pest controller on three occasions including clearing a wasps' nest from his garden months before. He refused to answer questions.
The mystery 999 call was made from a phone box in Braughing nearby and was only linked to the killing later that day.
The caller had asked for an ambulance for Holhock Cottage using one of several old spellings for the village, Furneau, before hanging up, the jury heard. Mr Latham said: "There is no Holhock Cottage, that is what the colonel's house used to be called many years before."
He said that the ambulance had driven along the road but could not find the address or see anyone about and logged it as a "hoax call".
At around the time of the call, a lorry driver passed a telephone kiosk in Braughing and saw a Land Rover Discovery or Range Rover, similar to cars Docherty-Puncheon often drove, nearby.
During a 25-year Army career the colonel, a Second World War veteran, was stationed in Canada, Nigeria, Germany, and Cyprus and travelled widely in the United States. After retiring he worked as an antiques dealer.
Docherty-Puncheon denies murdering Lt Col Workman and having a firearm with intent. The case continues.