"She was repeatedly stabbed to the neck and upper body and she bled to death as a result.
"The killer, who the prosecution alleges, was Stephen Nicholson, then left her either dying or dead in a large area of woodland and made his escape.
"It had clearly been the intention of her attacker to kill her, in other words, she had been murdered."
Mousley said that Nicholson told police after he was arrested that the night before her death Lucy had sent him a Facebook message telling him she was pregnant.
Nicholson had been friends with Lucy's stepfather Richard Elmes and worked with her mother Stacey White when he rented a room opposite the girl's bedroom, Winchester Crown Court was told.
Disturbing diary entries and letters discovered by Lucy's parents after her death revealed the extent of the alleged ordeal the schoolgirl was exposed to.
In a heartbreaking note entitled "abuse", she wrote that he would "He would make me or rape me anyway" and she also described how she was forced to lock herself in the bathroom of her home in Southampton, to avoid sex with him.
She warned him she "had a hold of him" in a row just days before her death.
He is said to have lured the girl to woodland at Southampton Sports Centre where he stabbed her neck and chest in a "vicious" attack on July 25 last year.
Several CCTV cameras captured Lucy making the final walk to her death, with the last one being a Tesco CCTV camera at 9.30am that day, as she allegedly went to meet Nicholson in woodland at the centre.
Jan Smallwood, who the prosecution say was the last person to see Lucy before she met Nicholson, said: "I was walking my terrier Lily and I saw a young girl.
"She was taking big steps and she seemed to be purposefully walking somewhere in a straight line. When I saw the CCTV footage of her that was released, I thought 'that was the girl I had seen'."
The prosecution said "compelling" evidence gathered against Nicholson showed he "had an interest in under-age sexual activity" and had a collection of knives.
Nicholson, of Southampton, denies Lucy's murder, three counts of raping her when she was 12, and two counts of sexual activity with a child when she was 13.
He also denies sexual activity with a child relating to a second victim at the scene of Lucy's murder five years earlier.
Where to get help:
• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline Safe to Talk on: 0800 044 334 or text 4334.
• Alternatively contact your local police station
• If you have been abused, remember it's not your fault.
