Trimaan Dhillon allegedly began stalking Ms Ruggles after she split with him
Lance Corporal Trimaan Dhillon, 26, is accused of murdering Alice Ruggles on October 12, last year.
He allegedly began stalking the graduate after she split with him because of his cheating.
Ms Ruggles, 24, was found with her throat cut at her flat in Gateshead in Tyne and Wear, just five days after she told police not to arrest him, Newcastle Crown Court heard yesterday.
Dhillon, 26, who is known as Harry and had ambitions to join the SAS, denies murder.
On the night she died, the jury was told he broke into Ms Ruggles’s home to meet her when she returned from work at a Sky sales centre in Newcastle.
The scene where Ms Ruggles' body was found
The court heard while he was obsessed with Ms Ruggles, who he had met online in 2015, he cheated on her with other women.
As he waited in her flat, he allegedly tried to arrange a “casual hook-up” with another woman on the Tinder dating site.
The soldier, who is from a Sikh background, is then alleged to have used a kitchen knife to cut her throat as she showered.
The court heard, after she had ended the relationship, Dhillon bombarded her and her family and friends with pleading messages.
Prosecutor Richard Wright QC said he was “utterly obsessed” with her.
He said: “From an early stage the defendant was abusive, controlling and manipulative.
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"Those who knew Alice knew a lively fun-loving girl whose personality changed in the months before her death as a consequence of her relationship with Harry Dhillon.
“She was withdrawn, isolated deeply troubled by his behaviour after she ended their relationship.”
Dhillon is accused of using his skills as a signaller with 2 Scots, the Royal Regiment of Scotland, to hack her emails, phone messages and social media.
The court heard Dhillon was obsessed with Ms Ruggles, who he had met online in 2015
Ms Ruggles reported him to the police when he drove twice from his barracks in Edinburgh to her flat.
Sadly the dilemma this young girl was left in is obvious
On the second occasion she was left terrified when he knocked on her bedroom window at her ground-floor flat at night to leave chocolates and flowers.
Northumbria Police took a statement and Dhillon was warned to stay away from her by the police and Army but he allegedly continued to send frightening messages.
The court heard she called the police again on October 7 last year and found the officer in charge of her case was on leave so it went to another police constable, who put the decision to arrest him “on her shoulders”.
Mr Wright said: “He put the decision on Alice’s shoulders: ‘do you want us to arrest him or not?’ Sadly the dilemma this young girl was left in is obvious. She was scared but she had cared for and even loved him at one time.
“She decided not to have him arrested and paid for that decision with her life five days later.”
The court was told that through his monitoring of her emails he knew Ms Ruggles was in contact with Mike James, an Army officer who was a friend of her sister Emma, also an officer.
Dhillon was left in a jealous rage, it was claimed, as the two forged a fledgling relationship after she had dumped him.
They were to meet the weekend she died. The trial continues.