The Orange Order has promised to mount a full investigation into claims that an Orangeman was involved in the murder of John Allen two weeks ago in Ballyclare.
His father, John Allen snr, resigned yesterday afternoon from the order, after 28 years in the organisation.
He has alleged that the man who targeted his son is a member of the Orange Order.
"This month has been the saddest of my entire life and today was extremely difficult for me," Mr Allen said.
"I did not want to do this as I have been proud to be a member of the Orange Order for 28 years, and my father was a member for 45 years.
"But I cannot belong to an organisation that also counts my son's killer as a member."
While he stopped short of naming the man, Mr Allen said he had been told the identity of his son's killer by a number of different sources.
"I know who it was but the police said there is not enough evidence. Why is it that these murders go unsolved?" he said.
"I visited the mother of the young Catholic boy who was beaten to death in Lisburn last night to offer my sympathies. No-one has been charged with his murder.
"Why is it so difficult to put these people off the streets?"
A spokesperson for the Orange Order said the allegation was a serious matter that would be thoroughly investigated.
"We understand that Mr Allen snr has made an extremely serious allegation against a fellow Orangeman in connection with his son's murder," the spokeman said.
"The institution will now mount a full and thorough investigation into Mr Allen's claims.
"In the meantime we urge anyone who has any knowledge of this appalling crime to co-operate fully with the PSNI in helping to bring the perpetrators to justice."
'Jock' Allen was shot twice in the head and the legs by gunmen at the flat he shared with this half-brother in Rashee Park, Ballyclare on November 8.
John Allen snr revealed that his son had been ordered to leave the town by the UVF one month before he was murdered.
