A jealous husband who could not accept the end of his marriage has been jailed for at least 23 years after stabbing his ex-wife to death in Cardiff. The court heard that his anger grew when she began dating a work colleague.
Thisara Weragalage, 38, killed his former wife, Nirodha Niwunhella, 32, on the morning of August 21, 2025. The attack happened on a quiet suburban street in Riverside, Cardiff. It was a place where people usually started their day in peace. Instead, it became the scene of a terrible crime.
Weragalage and Ms Niwunhella married in Sri Lanka in 2017. In 2022, they moved to the UK to begin a new chapter of their lives. At first, they lived together as husband and wife. But over time, their marriage began to struggle.
Ms Niwunhella found work at the Springbank Care Home in Barry. There, she met a colleague named James Stephenson. They became friends. As they talked more, she shared that she was having problems in her marriage. She told him her husband was physically abusive and that they were having “sexual issues,” the court heard.
As the friendship between Ms Niwunhella and Mr Stephenson grew closer, Weragalage found messages between them on her phone. He became increasingly jealous. According to Cardiff Crown Court, he started “spying” on her and tried to control who she spent time with.
The marriage continued to fall apart. In April 2025, the couple moved to separate addresses. After that, Ms Niwunhella and Mr Stephenson began a romantic relationship. By then, Weragalage had become deeply focused on his wife’s new life.
The court heard that he became “obsessed” with Ms Niwunhella and her new partner. He begged both Mr Stephenson and Ms Niwunhella’s father to help him fix the marriage. When that did not work, his behavior changed. He began threatening the couple as his desperation grew.
A message found on Ms Niwunhella’s phone showed how serious things had become. Judge Daniel Williams later quoted it in court. He said: “A message found on Nirodha’s phone, sent by her to a friend on July 10, said that you were threatening to kill her and James Stephenson.”
In the weeks before the attack, Weragalage visited Mr Stephenson’s address eight times. The day before the murder, he bought a pack of kitchen knives. Prosecutor Mike Jones KC told the court this was not random. He said: “The prosecution case is that such was the ferocity of the attack on her that the knife broke during the assault.
“His intention, the crown say, was a determined and planned intention to kill her.”
On the morning of August 21, 2025, Mr Stephenson was working a night shift. Ms Niwunhella left his address to go to work. It was early and the street was quiet. As she walked through the car park, Weragalage was waiting.
She was ambushed outside. The attack was violent and sudden. The court heard she suffered “extensive and catastrophic” injuries. She had 17 stab wounds and injuries to her neck, face, chest, and leg.
Mike Jones KC told the court: “Nirodha’s murder was not a chance encounter between her and the defendant. Rather, the defendant had been planning his fatal attack on Nirodha driven by the fact that she had clearly moved on from their relationship and his behaviour towards her.”
Ms Niwunhella was later found lying between two cars. The community in Riverside was left “shocked and saddened” by what had happened.
After the stabbing, Weragalage fled the scene. Later that morning, he was detained after trying to throw himself under a lorry. When questioned by police, he said he could not remember what happened after confronting his wife. He claimed he bought the knives only to scare her.
Andrew Taylor, defending, told the court: “He was obsessed by his wife and he was overtaken by jealousy. He could not live without her and he could not contemplate a future where he was on his own.”
Weragalage pleaded guilty to murder and possession of a knife in a public place. On Friday, at Cardiff Crown Court, Judge Daniel Williams sentenced him to life in prison with a minimum term of 23 years and nine months.
During sentencing, the judge spoke directly to him. He said: “You could not accept that your marriage was at an end. You could not accept Nirodha making her own choices to live a life without you. Nirodha’s relationship with James Stephenson became your sole and obsessive focus.”
Judge Williams described the attack as “ferocious” and said Ms Niwunhella had “no chance of surviving.” He added: “She has been described as the kindest and most caring person you could meet.
“She had a long and happy future ahead of her. Your brutal selfishness has left a void which can never be filled.”
Ms Niwunhella’s family later shared a tribute. They said: “We remember Nirodha as a cherished daughter, family member and dear friend to many.
“Nirodha will be forever remembered with peace, love and gratitude. She touched many lives with her kindness and warmth and her memory will continue to inspire us.
“Though her life ended too soon, the love she shared will always remain with us. Rest in peace angel.”
Emma Davies of the Crown Prosecution Service also spoke after the case. She said: “Thisara Weragalage planned his attack, visiting the area several times leading up to it and buying the murder weapon.
“His premeditation was a significant factor in this shocking murder.
“The strong evidence presented by the Crown Prosecution Service demonstrated his intention and resulted in a guilty plea.
“The Crown Prosecution Service are working together with the police to build strong cases against those who perpetrate violence against women and girls, and our prosecutors are making sure more victims of these abhorrent and devastating crimes receive the justice they deserve.
“Our thoughts remain with the family and friends of Nirodha, who have suffered a tragic loss.”
