An already-convicted murderer carried out the cold-blooded killing of a retired Army officer on his doorstep in a "whodunnit" case that has remained unsolved for eight years, a court heard on Wednesday.
Lieutenant Colonel Robert "Riley" Workman, 83, was gunned down on his doorstep in Furneux Pelham on January 7 2004.
The killing remained a mystery for years but now former pest controller Christopher Docherty-Puncheon is standing trial for his murder at St Albans Crown Court.
The 33-year-old, from nearby Stocking Pelham, has already been convicted of the murder of Fred Moss in late 2004, and is already serving a life sentence.
Prosecutor Richard Latham QC said this showed Docherty-Puncheon was capable of "cold-blooded killing".
He said the murder of Lt Col Workman, known by many as "The Colonel", was an "execution" in that vein, much like the killing of Fred Moss.
He said: "This is a whodunnit trial - there is no dispute that someone murdered Lt Col Workman, the question is are you sure it was this defendant?"
He went on: "It is a form of execution or at least a complete deliberate infliction of very serious bodily harm."
Opening the trial, Latham described a series of significant events in the hours before and after the murder, including a mysterious 999 call made from a telephone box in the village that made reference to a non-existent house in Lt Col Workman's street.
A lorry driver claims to have seen a car similar to Docherty-Puncheon's next to the phone box around the time the call was made.
Latham also claimed that telephone records from the night of the murder show that Docherty-Puncheon, who claims to have been at home on the night of the murder, rang his answering machine to check for messages that night.
He said: "You don't need to ring your answer phone to check for messages if you have the answer phone right in front of you.
"It was clear he was not at home."
The trial continues.