Former Sinn Féin MP Barry McElduff will not face prosecution over a controversial video he posted of himself balancing a loaf of Kingsmill bread on his head.
It was posted on his Twitter account on the anniversary of the Kingsmills atrocity.
Ten Protestant workmen were shot dead by the IRA on 5 January 1976.
The victims' families said they were "disappointed but not surprised" at the decision not to prosecute Mr McElduff.
The Public Prosecution Service (PPS) said there was insufficient evidence to "provide a reasonable prospect of conviction".
In a statement, Mr McElduff's solicitor said their client was "satisfied" with the decision of the PPS following the "unfortunate circumstances" of 6 January.
"As he did from the outset, Barry stated that any upset caused was unintentional," they added.
The solicitor said Mr McElduff had apologised for his actions and that the PPS decision "can perhaps now draw a line under the situation".
Mr McElduff later resigned following the incident but has always maintained he never intended to cause offence.
'Deep and unnecessary'
It was an eight-second video, posted shortly after midnight on 5 January 2018, which ended a political career of more than 20 years.
Mr McElduff accepted the video caused "deep and unnecessary" hurt to the families of the Kingsmills victims.
He apologised and resigned as MP for West Tyrone but he has always insisted that he in no way intended to cause hurt and the video was spontaneous and not premeditated.
He said at the time he was not aware the post coincided with the Kingsmills anniversary.
He was questioned by police about the improper use of a public electronic communication network, as was his party colleague Máirtín Ó Muilleoir who retweeted the video.
Mr Ó Muilleoir, a former finance minister, later apologised and told BBC News NI he "would not have tweeted" it if he didn't think it was "wholly innocent".
After examining the police file, the PPS decided no further action would be taken.
PPS assistant director Martin Hardy said there was insufficient evidence to provide a reasonable prospect of conviction.
"The PPS acknowledges the content of the video posted on the anniversary of the Kingsmills murders caused a great deal of hurt to those directly affected by the atrocity and many others in the wider community," Mr Hardy said.
"We have written to the next of kin of the Kingsmills victims and the attack's survivor to explain in detail the rationale for the decision.
"Whilst we recognise the outcome is disappointing to those offended by the content and timing of the video, we can offer assurance that these decisions were reached only after the most careful examination of all evidence and information available."
In a statement, the victims' families said: "Last year, the PSNI did not recommend prosecution when a suspect whose palm print was identified in the getaway vehicle was arrested.
"We would, on this occasion, have been more surprised if a prosecution had been recommended.
"Our confidence in the judicial system has been badly shaken, we feel as victims nobody seems to care. This decision is simply the latest in 42 years of disappointments."