British Ministry of Defence documents revealed that UK Special Forces officers suspected their men were killing unarmed Afghans who posed no threat. They also showed the allegations were kept secret and not reported to the Royal Military Police (RMP).
The court is considering whether the allegations were investigated properly by the armed forces.
The man bringing the case, Saifullah, claims four members of his family were assassinated in the early hours of February 16, 2011.
His lawyers were asking the court to order the defence secretary to release more documents before a full judicial review hearing.
Documents already disclosed were presented to the court. They showed nine Afghan men were killed in a raid on February 7, 2011 and eight more were killed by the same special forces assault team two days later.
More than a dozen detainees were killed after they were taken back into buildings to help search them.
British troops claimed they were forced to shoot them after they reached for hidden weapons.
The documents showed that in one email, a British lieutenant colonel expressed disbelief at the official accounts. He said it was “quite incredible” the number of prisoners who decided to grab weapons after being sent back into a building.
A week later, the four members of Saifullah’s family were shot dead in similar circumstances by the same special forces assault team.
The documents show the killings were described as “astonishing” by a senior officer.
Another senior officer later dismissed a soldiers’ description of events, saying “the layers of implausibilities” made the official account “especially surprising and logic defying”.
The court heard a British officer provided a written statement to a commanding officer after a member of the special forces told him all fighting-age males were being killed regardless of the threat they posed.
The officer said: “It was also indicated that fighting-age males were being executed on target inside compounds, using a variety of methods after they had been restrained. In one case it was mentioned a pillow was put over the head of an individual being killed with a pistol.”
All the anecdotal reports of unlawful killings were locked away in a top secret “controlled-access security compartment”, the court heard.
The court documents showed the allegations were raised with a “very senior officer” at UK Special Forces headquarters.
The special forces leadership did not notify the RMP. Instead, the high-ranking officer ordered an internal review.
It examined 11 raids where the special forces unit had killed people in similar circumstances in the previous six months. They had all been taken back inside buildings to help with the search after surrendering.
The final report was written by the commanding officer of the special forces unit accused of carrying out the executions. He accepted the version of events given in the official accounts of the raids.