The frightening trio in Halloween costumes who showed up on a Virginia family's doorstep were all just actors playing a role with their relatives getting in on the gag, according to the police.

The Alexandria PD released a statement on Facebook, saying they put in over 100 investigative hours looking into what they originally thought was a real-life horror movie that unraveled on the night of October 14 outside the house in Alexandria, VA.

But it turns out ... the incident was just a prank with three teens dressed in spooky costumes standing at the front door making threats to their relatives inside their abode. Doorbell video captured every harrowing moment — even when one of the masked characters furiously banged on the door, threatening to kill the homeowners if they didn't come out.

A woman named Shayla was staying inside the home with her mom, brother, and dog ... Shayla ironically told a local news station she thought it was just a prank at first and warned the trio to back off because the cops were on their way.

But the police said Shayla and her family were all in on the joke. Alexandria Police Chief Tarrick McGuire said the case "represents a serious moral failure" and pranks such as this one could have deadly consequences. Tarrick added parents must be accountable for their children and correct their behavior when it's required.

Case closed.