A 24-year-old karate black belt is currently on trial for beating his helpless girlfriend to death.

A court in Cardiff, Wales, heard that John Matthews told the police, “I’ve beaten her up and now she’s dead.”

Matthews’ girlfriend, Xixi Bi, also 24, was found lying on her back at her own home by cops and paramedics. Unconscious, she was rushed to the University Hospital of Wales, Mirror said.

Unfortunately, she was pronounced dead following cardiac arrest, Wales Online reported. Post-mortem assessment revealed she had “numerous and widespread” bruises. She also had jaw and rib fractures according to the examining pathologist.

Prosecutor Paul Lewis told the jury, “In essence, the prosecution alleges the defendant beat Ms. Bi to death in her own home in a vicious, sustained and prolonged attack. We submit he is guilty, not of manslaughter, but of murder.”

Lewis said Matthews tried calling emergency before 8:30 a.m. on August 19, 2016, from his home address, but ended up speaking to a police officer. He reportedly said on the line:

“Well me and her had a bicker last night and I have ADHD and I hit her a few times and we were ok and she was talking to me and we were fine and she fell asleep. Then I have been really horrible to her this last day and now she is struggling to breathe.”

Matthews claimed that he had a black belt in karate but was rather surprised to realize how hard he hit his girlfriend. He said he was “not that strong” and called the incident “a little hiccup.”

Lewis said Bi tried to defend herself, but apparently, she was simply overpowered. Matthews’ trial continues.