An inquest has heard how the south Armagh brigade of the Provisional IRA was reprimanded by the terror group's leadership for sectarian killings just six weeks before the Kingsmill massacre.
Responsibility for the sectarian slaughter of 10 Protestant workmen on January 5, 1976, was claimed by a group calling itself the South Armagh Republican Action Force.
However, the Historical Enquiries Team and the PSNI later stated that the attack was carried out by the Provisional IRA using a cover name.
At the time, the terror group had been on official ceasefire since February 10, 1975.
This week, the inquest into the atrocity resumed after being halted for almost a year.
Yesterday saw the third day of evidence from a PSNI intelligence officer identified only as J2, who spoke from behind a screen about connections between suspects in the Kingsmill massacre and other sectarian killings around that time.
Intelligence reports were read in Laganside Court in Belfast naming the 13 suspects thought to be behind the attack and their connections to other killings,
One intelligence report said a "severe reprimand" for sectarian killings had been issued by the Provisional IRA's army council to the south Armagh brigade six weeks before the massacre, although attacks on the security forces were allowed to continue.
"The brigade threatened to go alone and was supported by the Derry brigade," the report added.
Referring to an IRA leader as Article 2, it also said he "visited last weekend and met a brigade deputation".
"He was firm on the sectarian aspect but offered a supply of AK47s for use against the security forces," it explained.
Other reports offered details of the suspects linked to the atrocity, including one referred to as S91 who is said to be connected to 46 murders.
These included the killings of 22 civilians, including a seven-year-old boy, 21 soldiers, two police officers and another person.
The reports identified S91 as linked to the Kingsmill massacre and the killing of five people at Tullyvallen Orange Hall in September 1975 - another murder that was claimed by the South Armagh Republican Action Force.
Another intelligence report said S91 was a leading member of the ruthless south Armagh brigade and had been involved in the murder of policeman William Elliott and the murder of a UDR corporal.
A separate report from 1975 identified him as head of IRA operations in south Armagh with links to firearms, murder, robbery and kidnapping.
Representing some of the victim's families, Alan Kane QC noted a report stating that after S91 was imprisoned in 1976, there was no significant terrorist activity in the area for more than six months, "indicating that when S91 was not available, activity diminished".
The court also heard excerpts from a Republican Information Service news sheet praising a "swift action" by the south Armagh unit that killed three soldiers in an observation post in Crossmaglen before Kingsmill.
The news sheet ran a statement from the south Armagh brigade saying the action had been taken in retaliation for the harassment and the blowing up of cross-border roads.
J2 said: "This clearly indicates that the IRA were involved in that action on the day and they were responsible for it."
The inquest also heard a report that information about terrorist outrages in south Armagh had come from an interview with a "self-confessed IRA man", but the report said no action should be taken without the go-ahead from CID in Newry, the local regional crime squad and Special Branch.