Two officers with a Vancouver Island police department have been charged with the sexual assault of a "vulnerable" woman, authorities announced Tuesday.

The investigation into the members of the Central Saanich Police Service began on Oct. 28 after "a person came forward with information about two officers who allegedly had unlawful sexual contact with an adult woman they met while on duty," the Vancouver Police Department, which led the investigation, said in a statement.

Sgt. Matthew Ball, 43, has been charged with one count of sexual assault and one count of breach of trust.

Const. Ryan Johnston, 40, has been charged with one count of sexual assault.