A bloodied Daniel Grant then left her on the floor of their Grosvenor Road flat and went to the police station to confess.
When police arrived at the flat at around 11.15pm on April 11 last year, they found the body of Catherine Ogram, 35, lying in a pool of blood.
Thirty-two-year-old Grant could spend the rest of his life in a secure unit after admitting manslaughter on the grounds of diminished responsibility at Winchester Crown Court on Monday. He had denied a previous charge of murder.
Prosecutor, Oba Nsugbe, recounted the history of the relationship between Grant and Huddersfield-born Miss Ogram, known as Liz.
They met in 2000 and lived together in Farnham before renting a ground floor flat together at 35 Grosvenor Road.
Miss Ogram, who had a nervous breakdown on a previous trip abroad and was prone to bouts of depression, knew that Grant was a long-term user of drugs and a heroin addict.
Within a year of moving to Aldershot, Grant had given up his job as a labourer and used much of their joint benefit money to buy drugs.
He would move out of the flat for months at a time and spent most of his days in a nearby park with friends.
Mr Nsugbe told the court that police were often called to the flat following reports of arguments between the two, but on all occasions Miss Ogram refused to bring charges against Grant.
A week before her death she rang the police to say that Grant was behaving in a “strange manner”, but again she did not make a formal complaint.
The court heard that on the morning of the incident a friend of Grant’s saw the couple arguing.
Miss Ogram said that she wanted him to leave and, in a moment of frustration, said that she would put a bullet in his head.
That, Mr Nsugbe said, was a significant moment.
At 10pm that night Grant left a friend’s flat, where he had spent most of the day, saying that he was going to buy more drink. Instead, he went straight to the Grosvenor flat to confront Miss Ogram.
At about 10.15pm neighbours heard the noise of slamming doors coming from the flat, and a person jumping up and down.
Mr Nsugbe said that about an hour later, a bare-chested Grant entered the police station and said that he had killed his girlfriend.
The court heard from Dr Jason Fee, a specialist in mental disorder who had treated Grant at Ravenswood House, a medium secure psychiatric unit in Fareham.
He said that Grant, who is suffering from paranoid schizophrenia, had a long history of mental illness dating back to his teenage years.
Dr Fee said that in his opinion the disorder came first, followed by the drugs, which gave Grant a relief from the illness.
He added: “He is at high risk of future relapse and he poses a serious danger to members of the public.”
Judge Michael Brodrick raised concerns that there were clear warning signs of Grant’s mental problems, and asked if any lessons could be learnt from the case.
Prosecutor, Mr Nsugbe, said that a well-travelled Grant had left medical records with various authorities in different parts of the country.
The police had also been powerless to take further action against Grant following the numerous incidence of alleged violence against Miss Ogram.
Describing the case as “extremely disturbing”, defending barrister Anthony Chinn said that Grant was extremely fond of Liz and that he was sorry for what he had done.
Ordering Grant to be detained at Ravenswood House for an indefinite period, Judge Brodrick said: “There is very little left for the family of the deceased but to know that people are actively trying to stop this happening again.
“My sympathy goes to the relatives and friends of Miss Ogram, in particular to her parents. The loss of a child is a tragedy for a parent, but to lose a child in these circumstances is a parent’s worst nightmare.”