Vague recollections of a drive-in movie....help me with the title please

[Texdar]

Back in the 70's my family would go to a local drive-in that had a $1 a carload night on Friday nights. Pretty cheap entertainment for my parents, my two brothers and my two sisters.  Saw many horror films there, including Last House on the Left (didn't see all of it though as it was too disturbing for my mom and she really didn't want her kids seeing it).  

One movie I saw but can just remember bits of, was of a police investigation going on at a castle.  There were several chalk outlines of dead bodies and I believe they showed what happened in flashbacks but I can't be for  sure.  If anyone has an idea of what this movie might be,  I'd greatly appreciate it.  I do remember the castle was rather gloomy (but I guess most are).

Thanks in advance for any help.