TRESPASS on its own is NOT a CRIMINAL offence, It's a CIVIL MATTER. Therefore the police cannot bring the matter to a criminal court. Trespass can be a factor in other crimes, i.e. if you were carrying a gun, (armed trespass), intending to commit an act of theft, damage, or threats to kill, (burglary) etc, etc. The landowner (not the shooters) in this case could possibly take the matter to a civil court, but this is highly unlikely due to the high costs for little gained.
DO NOT worry about it.