Throughout the film, you know that someone is obsessed with the singer, and she is getting letters (kept secret at 1st) made up of cuttings about her getting killed.
In the end, you find out, that the mad fan is not actually the killer (just obsessed) and I think IIRC used as an acomplice, and the sister of the singer was actually involved with the appartent murder attempt.
She signed up an hitman to try to kill her sister, and throughout the film the bodyguard thinks its the fan etc, but isn't, turns out his ex-mate on the force.