Murder Case Solving in Prolog

%%prolog program to solve a murder

:-dynamic suspect/1.
suspect(bob).
suspect(mary).
suspect(john).

:-dynamic place/1.
place(bedroom).
place(hallroom).
place(kitchen).
place(road).
place(dining).

:-dynamic weapon/1.
weapon(knife).
weapon(rope).
weapon(pillow).
weapon(rivolver).

%%define the killer, murderplace,murderweapon
killer(john).
murderplace(hallroom).
murderweapon(knife).

%%%remove form the list,those who arenot killer,murderplace,weapon

iskiller(X):-
killer(X),write('-is the killer');
retract(suspect(X)),write('is not the killer.so removed from the list').

isplace(X):-
murderplace(X),write('-is the murderplace');
retract(place(X)),write('is not the place.so removed from the list').

isweapon(X):-
murderweapon(X),write('-is the weapon');
retract(weapon(X)),write('is not the weapon.so removed from the list').

answer(X,Y,Z):-
killer(X),
murderplace(Y),
murderweapon(Z),
write('murder solved').