The devastated son of triple killer Michael Atherton said he could not understand why "such a good man" would kill his partner and three relatives.
Michael Atherton Jnr lost his mother, Susan McGoldrick, 47, her sister, Alison Turnbull, 44, and his cousin, Tanya Turnbull, 24, in the tragedy in Horden, Peterlee, County Durham, on New Year's Day when his father blasted them with his licensed shotgun before killing himself.
Relatives released heartfelt tributes to those who died - including the gunman.
Michael, 17, released a joint statement on behalf of himself and his sister, Laura McGoldrick, 19, who managed to escape the slaughter by climbing through an upstairs window.
He said: "We are truly devastated. Me and my sister have lost the best mother in the world. We don't understand why my dad would do anything like this as he was such a good man.
"At the end of the day we have lost four loved family members and we hope they are all at peace now."
Mr Atherton's parents, Peter and Christine, said: "We and our whole family want to express our sympathies to the families of Susan, Alison and Tanya.
"Although we loved Michael, we are sorry for his actions and don't understand why he did what he did. We dearly loved Susan as a daughter for over 20 years and are devastated by the loss."
Relatives of the three women paid individual tributes to them.
In a statement, they said: "We as a family would like to take this opportunity to express our devastation at the loss we have suffered following the tragic events of Sunday evening and would like to pay individual tributes to each of our much-loved family members whom we have lost.
"Susan was a much-loved sister, who was adored by both family and friends. She was particularly close to her sisters and loved spending time with them.
"She was so caring and all that mattered to her was her family. We are shocked and shattered by what's happened.
"Susan loved her job in a local supermarket where she was held in high regard. She was very easy-going and was always laughing and joking.
"Alison was a fantastic mother, sister and partner who was always there for her family and friends when we needed her. She was a fantastic mam to her son, Bobby, and daughter, Tanya, always so caring and loving.
"Alison worked locally in Peterlee and loved nothing more than spending time with her family and loved ones. We are destroyed by the loss of Alison and struggling to come to terms with her death.
"Tanya was the most amazing daughter, partner and sister you could ever wish for. She was a popular, funny and a gorgeous girl with her whole life ahead of her, and we idolised her.
"Tanya and her boyfriend, Michael, were in the process of preparing for their life together and had plans to buy their first home. It was an exciting time for Tanya and she was always smiling and happy.
"This horrific loss is still sinking in and, as we are sure you can appreciate, we are devastated to lose Tanya in such tragic circumstances.
"We would also like to offer our heartfelt condolences to young Michael and Laura, who we know will be devastated by their loss.
"It's extremely important to us as a family that we are left in peace to grieve our loss and begin to recover from this.
"We would ask that the media respect our privacy and that we be left alone to comfort one another and attempt to come to terms with our devastating loss."
The shotgun murders have raised concerns about firearms legislation after it emerged Mr Atherton had his guns taken from him by police three years ago following concerns about his mental health.
He successfully applied to have his weapons returned after his family had raised concerns that he had threatened to shoot himself in 2008.
Durham Police confirmed that the weapons were taken from Mr Atherton's house as a precaution, but as he insisted there had been no threat to harm himself, they were returned. That decision followed national procedure, a force spokesman said.
"It was one person's word against another," he said. "If there was no grounds for applying for the revocation of a firearms licence the guns would be returned to the firearms licence holder."
Durham Police has voluntarily referred the case to the Independent Police Complaints Commission (IPCC), as the force had previous contact with the family.
Prime Minister David Cameron's official spokesman said the government had no plans to revisit UK gun laws which were "amongst the toughest in the world".