The killer: He met girl, 14, on internet and offered to pay her for sex

Mark Simpson now faces a minimum of 20 years behind bars after inflicting up to 40 injuries on his infant victim.

At the trial, Alexis' mother, Ilona, said Simpson was often depressed and would regularly burst into tears.

However, the judge described Simpson as "devious and deceitful" and his crime as "violent and abhorrent".

He added: "How you were able to act in such a wicked and abhorrent manner towards a helpless infant is beyond the understanding of all right-thinking people."

What the jury did not know was that Simpson had sent indecent photos and video clips of himself to girls as young as 13 whom he had met over the internet.

The 29-year-old tried to coerce girls into sending indecent photos of themselves to him, then asked them to meet for sex.

In an internet conversation with one 14-year-old, he said he would pay her to have sex with him.

Police discovered the chats as they inspected Simpson's computer while investigating Alexis' death.

Some of the internet conversations took place while Ilona and Alexis stayed with him at his home in Aberdeen's Deansloch Crescent.

He was jailed for 14 months, and placed on the sex offender's register, following a trial at Stonehaven Sheriff Court earlier this year.

However, the case could not be reported on until the end of his murder trial to avoid influencing the jury.

Simpson, who was originally accused of approaching 17 girls, is now serving a life sentence for the murder of baby Alexis.

It was alleged he had sexually assaulted two women and sent menacing and sexualised texts to another.

However, those allegations were eventually dropped after he admitted terrorising four girls, aged between 13 and 15.

He confessed to using messaging services and the phone to have indecent conversations and to sending lewd photographs and video clips of himself to the girls.

Most of the conversations took place at Deansloch Crescent, where he had set up home with Ilona and Alexis.

Simpson is now on the sex offenders' register after he admitted indulging in lewd, indecent and libidinous behaviour and practices with the girls.

Simpson's jail term would have come to an end next month.