A couple who lied over how their baby son died were months from prosecution under new homicide laws, police say.
John Boswell, 22, and Emma Buck, 20, were convicted of perverting the course of justice after the death from shaking in January 2005 of baby Ryan Boswell.
In March of that year, a legal "loophole" which allowed those accused over the death of a child to remain silent or blame each other was closed.
Boswell and Buck, from Shotton, Flintshire, had denied harming Ryan.
The pair were convicted at Mold Crown Court on Wednesday following a week-long trial. They will be sentenced on 6 June.
Ryan was in his parents' care for just 18 days before he was returned to hospital on New Year's Day, 2005.
He had suffered a brain injury consistent with being shaken and died 17 days later.
The court heard his injuries were so severe that to have happened accidentally, the baby would had to have been involved in a high-speed road accident or have fallen from a first floor window.
The prosecution said no-one else was at the flat at the time and one or other of his parents must have been responsible.
North Wales Police was unable to charge either parent over the child's death and instead charged both with perverting the course of justice for covering up what happened.
'Impossible to prove'
Police have said that if the offence had taken place months later, the pair could have been charged with the new offence of familial homicide.
Detective Superintendent Peter Challinor, who led the investigation, said: "These have always been the most difficult investigations you can do in the police.
"There's only two people responsible - the parents of the baby and they both deny anything has happened.
"Historically, it's been impossible to prove in most cases which one, if not both, committed the act and that was our problem here.
"The law was changed a couple of months after this to cover this loophole and if it happened after March of that year they would have been charged with a homicide offence.
"The law at that time didn't allow us to do so and the only proceedings we could put to them was the covering up of Ryan's death."
In November 2006, 21-year-old Rebecca Lewis from Swansea became one of the first people in the UK to be convicted under the new offence of familial homicide.
She was jailed for six years for failing to prevent her baby son Aaron Gilbert's murder in May 2005 by her partner Andrew Lloyd.
Consultant paediatrician Dr Heather Payne said it was important to identify those who could potentially harm their children at an early stage.
She added: "Sadly, about 20 children per year in the UK die in this way. It's really important that all the agencies look out for the things which might be pointers to problems.
"Everybody gets frustrated with babies, the trouble is some people go too far and lose control momentarily - that's still abuse.
"Our job as agencies is to identify people who are at risk and need more support and to make sure we prevent these things happening."