This came from a Brown Tree Snake Boiga irregularis. The relative width of the head, large eyes and arrangement of temporal scales in particular, confirm this. It is rear-fanged but not dangerous.
If you examine it, there will be a loreal scale present – a scale located between a pre-ocular scale and the nasal scale (which contacts the nostril opening). This is present in Australian Colubrid snakes but not in Elapids. Note: If the skin has dried out and likely to tear if you manipulate it, give it a light spray with water and allow it to soften (a tip from Sdaji).