A "guilt-ridden" mother who confessed to murdering her baby son while in prison for killing her young daughter has been jailed for life.
Lesley Dunford, 37, smothered seven-month-old Harley Dunford in his cot at their home in England on August 27 2003, six months before three-year-old Lucy died in similar circumstances.
However, Harley's death was not treated as suspicious until Dunford admitted the killing to prison staff in 2014 while serving seven years for the manslaughter of her daughter, the Old Bailey heard.
Jailing the mother-of-three for a minimum of 13 years, Mr Justice Baker said: "The reality is, had you not confessed to killing Harley whilst in custody, it is highly likely there would not have been a police investigation into his death and you would not have faced prosecution for murder."
Dunford had pleaded guilty to the murder of Harley at the three-bedroom home she shared with her husband Wayne in Camber, near Hastings, East Sussex in England.
Prosecutor Philippa McAtasney QC said she was only charged after making a series of confessions to staff at Drake Hall women's prison in Staffordshire in June 2014.
Before then, Harley's death had been put down to staphylococcal pneumonia and no action was taken.
When Lucy died in "very similar circumstances" on February 2 2004, the defendant turned to her local vicar and said: "It's happened again, it's happened again."
At the time of both killings, Mr Dunford, 58, had been out of the house at work, the court heard.
It was not until a coroner expressed his concern at Lucy's 2009 inquest that the decision not to prosecute over her death was reconsidered.
The medical evidence was reviewed and Lucy was found to have died from asphyxiation, the court heard.
In June 2012, Dunford was jailed for seven years after being found guilty of Lucy's manslaughter at Lewes Crown Court.
It was while she was serving her sentence that she admitted involvement in both deaths to prison staff, saying she was "riddled with guilt".
She told officers that she had been having "flashbacks and nightmares" about what she had done.
In a written confession, she stated: "I remember the day very clearly, the time I put Harley back to bed at 9am, after I had given him his breakfast. I was settling him down in his cot. I put him on his tummy and put his dummy in.
"But then something clicked in my head and I went back into the room walked over to his cot and pushed his face into the mattress until he stopped breathing.
"And then I put his head to the side and noticed there was blood and foam coming out of his nose. That's when I knew I had hurt him and I don't know why I had done it."
She went on: "Even though we had a death certificate I know I contributed to his death because I relive it every day."
Medical experts who reviewed the examination of Harley's body rejected the original finding.
Instead they found his death was consistent with asphyxiation and should have been recorded as unascertained, the court heard.
In mitigation, Alan Kent QC said the case was "quite extraordinary" and his client wished to convey her "sincere regrets and apologies".
He told the court that Dunford's husband, who is in the process of divorcing her, had forgiven her and "wishes her well in the future".
Mr Dunford, was was in court, had suggested that his "gullible" wife should be in a hospital and not a prison where she might be "bullied and taken advantage of".
Mr Kent said that Dunford, who had later moved away, had low intelligence and complex mental health problems including an "extremely emotionally unstable personality disorder".
Detective Chief Inspector Wendy Burton, of the Surrey and Sussex Major Crime Team, said: "This has been a tragic case in which two children have lost their lives and their family has been stricken by terrible heartache.
"Both investigations were complex. A key factor in both was forensic evidence, and in cases of very young children that can be very difficult to interpret in a way that the criminal justice system can deal with.
"But Lesley Dunford then confessed, on several occasions, verbally and in writing, to killing Harley too. This, together with the forensic review, was fully considered by the CPS who authorised her prosecution.
"Justice has now been done and our sympathies are with little Harley and Lucy."
Mr Dunford added: "This has been a very difficult time for myself. Lesley lied to me about what had happened with the children.
"She was very good at this and I would like to take this opportunity to apologise to family and friends for this deceit that lasted for a decade. I am truly sorry."