An investigation has found that there was no conclusive evidence that teachers at a north Belfast school were put under surveillance.
Members of the NASUWT union at St Patrick's PS had made the allegations.
That was after a man, who later disclosed he was highly trained in surveillance, was seen taking photographs of staff on a picket line at the Pim Street school.
He was later revealed to be a relative of the school's principal.
BBC News NI has obtained a copy of the independent investigation report into the teachers' claims.
A number of NASUWT members at the school took several days of strike action between November 2018 and April 2019, due to a dispute with school's management.
They subsequently claimed that they had been put under surveillance as a man had photographed or filmed the picket on some of the strike days.
The Council for Catholic Maintained Schools (CCMS), school governors and unions commissioned an independent investigation into their claims.
It was carried out by the former general secretary of the NIPSA trade union John Corey and Sinead McNicholl.
The NASUWT initially raised the staff's concerns about a man photographing the picket in November 2018.
In December 2018 and January 2019, the investigation report revealed, teachers became concerned that the man alleged to have filmed them was also involved in an incident at an eviction in County Roscommon in the Republic of Ireland.
However, the NASUWT later accepted that was not the case and there was no link to the Roscommon incident.
It later emerged that the man alleged to have been filming staff was married to the school principal's sister.
"Later it emerged that the man present at the picket line taking photographs was a relative of the school principal and a person with expertise in private investigation and surveillance," the report said.
In April 2019 the man, using the initials DFW, sent an email to the NASUWT explaining that he had gone to the school on strike days to ensure his partner's daughter could safely cross the picket line.
She was being employed as a substitute teacher in St Patrick's PS on some of the days that the NASUWT members were on strike.
Extracts from DFW's email were included in the investigation report.
"My wife was very concerned about her welfare and intimidation entering a picket line going into the school on the strike days," DFW's email said.
"At the last moment I decided to accompany my wife looking after her daughter's welfare."
"I am trained in surveillance at a very high level and would not be sitting in full view if I was employed to carry out work."
"I was never employed by any persons or relatives to take photos."
The school's principal told the investigation report's authors that her family life and career had been affected by the allegations.
She also told CCMS that "she did not commission surveillance, that she was not responsible for the actions of her sister or her sister's partner, that there was nothing untoward".
Incident caused 'upset and concern'
The investigation report concluded that it was reasonable for NASUWT to raise concerns that the teachers on the picket line had been under surveillance.
However, it also found that "there was no evidence available to enable the panel to conclude that the staff were subject to surveillance".
"The panel was satisfied that the employer was not involved in any manner in requesting any person to undertake surveillance of staff."
"There was not evidence available to enable the panel to conclude that the photographing/filming was done on request or for some other purpose."
However, the investigation's authors also concluded the incident had caused upset and concern to the striking staff and NASUWT officials.