The family of Michaela McAreavey has said criminal investigations have ground to a halt.
The newly-wed, 27, a teacher from Co Tyrone and Mickey Harte's daughter, was murdered in her honeymoon suite in Mauritius in January 2011.
Two men were cleared of the murder during a seven-week trial almost two years ago but the victim’s relatives claimed the Mauritian authorities had been reluctant to keep them updated since then.
A family statement said: “It was promised by the Mauritian prime minister that justice would be done and would be seen to be done in this case.
“However, as time marches on and the criminal proceedings seem to have ground to a halt, this promise is ringing hollow.”
Thousands of mourners attended Mrs McAreavey's funeral near her family home in Ballygawley, Co Tyrone.
She had married John McAreavey just 12 days before her murder and was buried in her wedding dress.
The statement said the McAreavey and Harte families were more determined than ever that justice be done.
It added: “They are hoping that a settlement can soon be reached with the hotel in respect of the civil proceedings but they are growing increasingly frustrated by the slow progress of the criminal proceedings.
“In particular, they have been disappointed by the reluctance of the Mauritian authorities to keep them updated with developments.”
The McAreaveys were celebrating their marriage at the Legends Hotel when Mr McAreavey found his bride dead in the bathtub of their room. She had gone back to their room from a poolside restaurant to get biscuits.
When she did not return her husband went to the room and found her body. She had been strangled.
Police said she was murdered after disturbing thieves in her room.
Five hotel workers were arrested over the murder before two were charged but cleared during a marathon trial at the island’s Supreme Court in the capital city of Port Louis in summer 2012.