A man has been found guilty of raping and murdering his niece before putting her body in a deep freezer.

Mujahid Arshid killed Celine Dookhran, 20, at a house in Kingston upon Thames, south-west London, in July last year, after spending months planning the attack.

He was also found guilty at the Old Bailey of the attempted murder of a second woman, who managed to escape.

Arshid, 33, was convicted of historical sexual assault offences against the second woman, who cannot be identified. He was sentenced to at least 40 years in prison.

A statement read out in court from Dookhran’s mother, Iman, said her daughter “fell victim to pure evil” and that “coming to terms with her death is likely to be a lifelong assignment”.

“She will always be there in the darkness that surrounds us,” she added.

Arshid’s co-accused, Vincent Tappu, 28, was cleared of kidnapping charges.

The jury heard that Arshid, a builder, had become increasingly obsessed with both women, and decided to kill them after discovering they had boyfriends.

Celine Dookhran, who was murdered by her uncle. Photograph: Metropolitan Police/PA

There had been tensions in Dookhran’s Muslim family over the fact that she had a boyfriend, and she had temporarily moved in with Arshid. He took the women to a six-bedroom house he was renovating and attacked them.

Members of Dookhran’s family shouted “Yes” when Arshid was found guilty of murder, attempted murder, rape and kidnapping. He had denied the charges.

The second woman, who had to undergo major surgery after the attack, gave extensive evidence from behind a screen during the trial. Arshid had cut her throat, inflicting a similar injury on Dookhran.

She told police about the attack from her hospital bed, and Dookhran’s body was found soon after.

As the jury returned its verdict, Arshid shouted: “I will prove that bitch wrong.”

In his defence, Arshid claimed the second woman had been responsible for the attacks and accused her of lying to the court.

Jurors heard that four years before the murder, Arshid had sent a series of messages to an undercover police officer, describing a rape fantasy involving the second woman. During their explicit exchanges, he said: “These kind of girls deserve rape – lol.”

Messages read out to jurors included ones showing Arshid asking the detective if he would like to drug and then force a teenage girl to have sex. He had also sent the police officer a photograph of the second woman, who was then a teenager. The messages were traced to his house.

When confronted by police, Arshid blamed an employee for using his computer and the case was dropped by prosecutors.

The court heard that the second woman only escaped the Kingston house after pretending to Arshid that she was in love with him. In her evidence, she said: “I started saying things he wanted to hear – ‘I love you, we can run away together, we can be happy together, we can have a family.’”

She told the court: “I’m not going to lie, I was scared for my life. I thought, if we get out alive, he cannot get away with this.”

She said she convinced Arshid she would run away with him and not tell anyone about Dookhran’s death, while secretly texting her mother for help. After she escaped, Arshid fled to a Holiday Inn in Folkestone, Kent, where he was eventually arrested.

In a conversation on WhatsApp with his wife, he said he was going to Pakistan.

The prosecutor, Crispin Aylett QC, told jurors that Dookhran was “dragged into his warped yearnings” after she moved into Arshid’s house. The Barclays bank worker, who was also an aspiring makeup artist, had told her boyfriend that she found Arshid “creepy” and a “pervert”.

Aylett said Dookhran was found face down in the freezer at an “awkward angle consistent with her having been stuffed inside”, with her arms covered in blood. Her body was extremely cold and she had obviously been dead for some time, Aylett told the court.

In the weeks leading up to the killing, Arshid carried out research on the internet and was inspired by the acid bath killer, John George Haigh, who was hanged in 1949 for murdering six people.

Mujahid Arshid at New Malden train station, as he waits with his luggage prior to boarding a train traveling to Folkestone. Photograph: Metropolitan Police/PA

The jury deliberated for 14 hours before delivering the guilty verdicts.

DCI Sam Price described Arshid’s actions as a “sexually motivated attack of unspeakable violence and horror”.

She added: “Celine’s family have been forced to sit through weeks of reliving their daughter’s last hours and they have done this with absolute dignity. Their distress has been compounded by the fact Arshid was someone they knew and trusted.”