Kasim Davey was discharged as a juror in the trial in December when he wrote on Facebook: "Woooow I wasn't expecting to be in a jury Deciding a paedophile's fate, I've always wanted to Fuck up a paedophile & now I'm within the law!."
He denied posting the message – which is in breach of laws on contempt of court – when initially questioned by the judge at Wood Green crown court in London. Davey was a juror at the trial of Adam Kephalas, a convicted child-sex offender who was given a suspended 12-month prison sentence in January this year.
Davey will now be prosecuted by the attorney general for "an act likely to interfere with the due administration of justice".
The attorney general, Dominic Grieve, was given permission to pursue the contempt case at a short hearing at the high court in London on Wednesday morning.
The two high court judges, Lord Justice Goldring and Mr Justice Ouseley, did not set a date for the next prosecution hearing.
Grieve did not attend court as he was at St Paul's cathedral, less than a mile away, for the funeral of Lady Thatcher.
The case is the latest in a string of contempt prosecutions involving jurors and members of the public using the internet to discuss ongoing criminal trials.
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