I feel may be couple of people attacked the Girls and ransacked the room and must used some material causing some small explosion material,culprits must have draged the girls on the staircase and some of the must have been bleeding on their head which must have been marks on the walls.

If it was gas leak,first Kitchen must have caught fire,all things in kitchen are neat.

As per the scene of Crime we need some finger print expert to get some impressions and match with the victims.

Balastic expert to know the material used in the explosion.