Let Me Inside

A detective is called out to a crime scene where someone was horribly murdered, but there seemed to be no tracks or evidence left behind, as if the killer had miraculously hidden every trace of his existence, the only slight clue of a break-in being an opened window, but the idea was quickly thrown out since the incident took place on the 9th floor of an apartment complex. With much to analyze, you decide to rent out a cheap house on the outskirts of a nearby town to be closer to the scene, but the landlady sure gave you the creeps, talking cryptically about a certain "it" you should watch out for… And you soon realize what she was referring to as the nights grow darker by the day, sending chills down your spine.