AN 18-YEAR-OLD man is in a critical condition after being stabbed in the chest in an unprovoked attack in Bournemouth's Lower Gardens. Detectives have now launched an investigation and are appealing for witnesses or anyone with information to come forward. Dorset Police received a report that at around 11.50pm last night an 18-year-old man had sustained a stab wound to the chest after being assaulted in the Lower Gardens in the town centre. The victim had been walking in the gardens toward Bournemouth Pier with two friends when they walked past a man and a woman who were sitting on a bench.