Garda sources said the contents of the envelope have not yet been seen as the envelope was immediately preserved for evidence and sent to Technical Bureau headquarters in Dublin for forensic examination.
It was found yesterday by members of the bureau during their examination of the Hawe house. It is understood the envelope was marked to be opened only by relatives.
“An envelope has been found in the house that is believed to be very relevant to the case,” confirmed a garda source.
“For the preservation of evidence it is being sent to the bureau for analysis, which will authenticate it and its authorship.”
The source said the contents are not yet known: “It may assist and it may not, depending on what it contains. It may give a sense of direction. We have to wait and see.”
Once opened, a working copy of the note is expected to be provided to the investigation team in Ballyjamesduff.
Garda sources said they were continuing with all aspects of a major investigation into what they consider was a “planned” murder-suicide.
Gardaí are speaking to friends, family members, neighbours, teaching colleagues, and associates of the couple in a bid to build a picture of their lives leading up to the mass killing.
Mr Hawe, deputy principal at his local national school in Castlerahan, is believed to have used a knife to kill his wife and three sons before hanging himself in the early hours of Monday.
“We have four people, three children, murdered,” said a garda source. “It’s a murder investigation, even though the perpetrator is dead.”
Gardaí suspect that Mr Hawe planned the murders. “He sat down and planned this: It was not blind rage,” said one source.
The discovery of a note pinned to the back door — warning callers to contact gardaí — followed by the envelope inside the house supported this, said the source.
“If he planned to kill his wife, he planned to kill his children as well,” said the source.”
Gardaí suspect the children were killed in their sleep.
Sources believe Mr Hawe probably killed his wife, Clodagh, first, then his eldest son (Liam, 13) who had his own bedroom, before murdering his two youngest (Niall, 11, and Ryan, 6) who shared a bedroom.
The couple and their kids were seen at various events in the locality on Sunday and appeared to be very happy, gardaí had said.
“The big question is why? Why and why now?” said one garda source.
“There must be something there, some build-up as his thinking got darker and darker, or some event triggered it,” said the garda.
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