The Special Criminal Court has been shown a letter written to State supergrass Russell Warren by John Gilligan seven months after the murder of Veronica Guerin.
Writing from Belmarsh prison in London where he was fighting extradition to Ireland, Mr Gilligan insisted he had done nothing wrong and would continue his legal battle.
The letter asked Mr Warren to ring Mr Gilligan's brother Thomas to check if his wife Geraldine was okay and also inquired about details of bets he had asked Mr Warren to place on his behalf.
The court was told that gardai followed Mr Warren to a later meeting with Thomas Gilligan because the witness was afraid that "something might happen".