Though the shrieks of butchered victims, maniacal cackles of murderous psychopaths and the groans of tortured specters were replaced by the giggles of trick-or-treaters, a horde of Boston history buffs primed to be spooked descended into darkness at Beacon Hill to explore the area’s history of carnage and mayhem.

Dressed as sexy French maids and Disney’s most honored heroes, tour guides departed from the State House steps last night to lead groups through streets of Beacon Hill with a BOO! – formerly called Murder and Mayhem – that leads the city’s fearless through the area’s most hair-raising and blood-curdling murder scenes.

“Tonight, the ambience on the hill and getting into costume is so great,” said tour guide Gretchen Grozier. “Even as a Boston by Foot guide, you see something new every time you walk somewhere.”

Dressed as a colonial Puritan in a stiff, gray dress, white bonnet and apron, Grozier led a group from the statue of Mary Dyer outside the State House to the home of the Dr. George Parkman, whose dismembered body was discovered rotting in the depths of a sewer after a Harvard professor who owed Parkman a sizeable debt bludgeoned him to death with a piece of wood.

At a nearby home, Grozier told a story of passion and bloodshed when in 1964, a pregnant young woman who was part of an affluent Beacon Hill family shot her boyfriend in the head and left his body locked in her room before fleeing the country.

Nearing dusk, bloodthirsty tourists down the street explored an alley said to be stalked by the ghost of a 19th Century murderer, who slit his mistress’s throat from ear to ear, covered her with bed sheets and set her corpse on fire — all while allegedly sleepwalking.

Though tourists said they were sufficiently spooked by the gruesome murders and tales of intrigue, they said they enjoyed learning about the grisly history of a seemingly spotless Beacon Hill.

“I liked seeing the houses that got really decorated, and the murders that happened in the houses that people still live in,” said Mystic Valley Charter School junior Angela Stigliano, who dollied up for the occasion with black and orange stockings.

Underneath a bent witch’s hat and with a glowing pumpkin lantern in hand, Michele Drury, a member of Boston by Foot, said she was excited for an ensuing paranoia on her first Halloween tour.

“The tours have been really informative so far,” Drury said. “Living in Boston, we take things for granted, but it’s great to find the story behind it.”