An allotment holder who strangled an elderly widow with a lawnmower flex has been jailed for at least 19 years.

Rahim Mohammadi killed 80-year-old Lea Adri-Soejoko because he feared he would be thrown off his plot at Colindale allotments in north London.

Adri-Soejoko, the allotment secretary, was found dead in a locked mower shed. Police had followed the sound of her ringing phone after her family had raised the alarm last February.

Mohammadi, 42, from Hackney, east London, was found guilty of her murder following a retrial at the Old Bailey.

Sentencing him on Friday to life with a minimum term of 19 years, Judge Richard Marks QC said: “How bitterly ironic that the place she loved so much – the allotment – was the place she met her death.”

Mohammadi, a regular opium user, killed Adri-Soejoko in a “violent loss of temper”.

The judge said: “It goes without saying although Lea was fit for her age, she was an elderly lady and as such, confronted and attacked by you as she was, was vulnerable in the extreme.”

Earlier, Adri-Soejoko’s children, Mark and Tess, spoke of the “torturous” road to “justice and truth”.

Facebook Twitter Pinterest Lea Adri-Soejoko. Photograph: Metropolitan Police/PA

The pair said their “happy and vital” mother was having fun and living a full life before Mohammadi “stole her from us”.

Her murder had nothing to do with the immigration debate, Mark Adri-Soejoko said, adding: “Some people make a play about the fact he is an immigrant or refugee, but it’s not to do with that. Where they come from has nothing to do with it. We are the children of immigrants. This is about the actions of one wicked individual.”

Tess Adri-Soejoko added: “Hatred is something you kind of rise to in a situation like this. I’m just glad that the truth has been revealed about him and who he truly is. I’m just glad he is not free and will not be able to do this to anybody else.”

The court had heard that Mohammadi, a Kurdish Iranian, had been involved with the allotment since 2008 through Freedom from Torture, an organisation helping torture victims suffering from post-traumatic stress disorder.

In September 2016, he clashed with Adri-Soejoko at an allotment association meeting and he called her a “bloody old witch”. Then in February 2017, Mohammadi beat her up on the allotment, causing bruises and fractures to the ribs. He then throttled her with the mower flex to stop her from reporting the attack, which would have led to his eviction.

John Price QC, for the prosecution, said: “Mrs Adri-Soejoko was beaten up. That in turn does point to a motive for her murder – to avoid detection for a shocking and very serious assault on a vulnerable old lady.”

The victim’s body was locked up in the mower shed, to which only four keyholders had access – including Mohammadi and Adri-Soejoko, whose set was in her pocket.

The prosecution said Mohammadi had planned to move her to avoid suspicion being cast on him, but police following the sound of her ringing phone found the body before he could act. His DNA was found on the cord used to strangle her and he was caught on CCTV coming and going from the allotment, jurors were told.

The court heard Mohammadi sought political asylum in Britain in 2005 and was given indefinite leave to remain in 2010.

DCI Noel McHugh, from Scotland Yard, said: “Although I never had the privilege of meeting Lea, we have learnt what a lovely, caring lady she was, like everyone’s mum or gran. She was a real pillar of the community, a sprightly 80-year-old grandmother who was very active in her local neighbourhood and secretary of Colindale Allotment Association.”

He said Mohammadi was a “manipulative, evil, controlling individual”.