A woman who suffocated her father, an MS patient, to death with a plastic bag was jailed for life on Thursday.
Claire Darbyshire, 36, who was the sole carer for her sick father, Brian Darbyshire, claimed the killing was part of a planned suicide pact after his multiple sclerosis became "intolerable".
Recorder of London Nicholas Hilliard QC, sentencing, ordered her to serve a minimum term of four years.
He said he accepted Darbyshire believed she was carrying out an act of mercy: "I accept your evidence that your father did raise the question of ending his own life and he wanted to do that and wanted your help to do so."
The killing was still unlawful, he added.
Police found the 67-year-old's body on 10 September 2015 at the family home in Dagenham, east London, dressed in a suit and next to several notes.
In one letter, Darbyshire had written: "Dad couldn't go on any more being bed-bound. He asked me to help him end it. Now I have to end it too as my action is claimed as a crime.
"If it was an animal then you would stop its suffering, but when it comes to a member of your own species you want to prolong the suffering as long as possible.
"We have the cheek to call ourselves civilised. Don't waste your time looking for me. My phone call to the district nurse was my last action."
The court heard Darbyshire took a train to Dover and was found wandering the cliff tops in Kent, asking for help following a decision not to jump.
Paul Keleher, Darbyshire's defence lawyer, argued her actions amounted to assisting suicide rather than committing an unlawful killing.
But the jury rejected the lesser offences of manslaughter and assisting a suicide and found Darbyshire guilty of murder last month.
In a statement, Detective Inspector Sarah McConnell, the investigating officer for the Met's homicide and major crime command, said: "It is always difficult for those involved when a person loses their life, whatever the circumstances, and this case raises a number of sensitive issues.
"The reclusive lifestyle that Brian and Claire Darbyshire had lived for a number of years means it is difficult to fully understand their precise situation. However, after considering all of the evidence in this case the jury returned a unanimous verdict of murder, which has been welcomed by the remaining family of Brian Darbyshire."
Darbyshire, who is transgender, is being held in a men's prison, according to the BBC.