A father who killed his seven-week-old son has been jailed for 12 years.

Brian Penn was convicted following a trial of inflicting blunt force trauma on Kaleb Penn’s head and body by unknown means and compressing his body on November 1, 2017 at a property in Ayr.

The baby was left so severely injured that he died two days later at the Royal Hospital for Children in Glasgow.

Penn, a former soldier, was also found guilty of assaulting Kaleb to his severe injury and to the danger of his life on various occasions between October 13 and 31 that year at a property in Ayr and elsewhere.

The 30-year-old had lodged a defence of incrimination blaming the child’s mother for the death.

Lord Weir sentenced Penn to 12 years behind bars when he was sentenced at the High Court in Glasgow on Wednesday, appearing by video link from prison.

He said: “When Kaleb was born on 11 September 2017 he could have expected without realising it the loving parental care and nurture so important for helpless infants.”

He said that Kaleb instead received the “very antithesis” of the care expected and “his life was instead cut short at seven weeks”.

Penn was originally charged with murder and attempted murder but was found guilty of culpable homicide and assault following his trial at the High Court in Glasgow.

Lord Weir said: “The nature of these offences and the circumstances of their infliction against a vulnerable baby now lost forever to his wider family fully justify a significant sentence.”

Brian McConnachie QC, representing Penn, said he is a first offender who has so far lived his life as a useful member of society, has served in the armed forces, and has a “good work ethic and was trying to support his family”.

He said the reasons for what happened will never be known.

He told the court: “There seems little doubt that the oddities of this particular case are that there was a significant body of evidence which supported the fact that Mr Penn and his partner were very pleased by the fact they were having a child and everyone who saw them acting together or separately with the child thought they seemed to portray a picture of family happiness, and quite how matters turned out as they did is something we will never understand the rationale for.

“The evidence suggested that there were very limited times when Mr Penn was in charge of Kaleb but as Mr Penn fully realises, the ladies and gentlemen of the jury returned the verdict they did and he will be sentenced on that basis.”