Inspector Lee found an unmarked white envelope at his desk. No one knew where it came from and who put it there. In it was a flash drive with a single video file. He didn't dare play it at work.

He took his laptop played it in his car at lunch.

It appeared to be a mishmash of various security cam footage edited into a single video. The time stamps were all over the place. The days rolled forward and backward. Some had no time-stamps at all.

The only thing they had in common was that they showed the same girl. Inside his house, at his work desk on his day off with no one noticing her. Rifling through his desk, dancing around his kitchen. ...wtf?

He looked away and back for a second, and suddenly her face was filling the monitor. The girl looked right at the camera. 

"Hey Lee... I can see youuuu..". She sing-songed. Then disappeared.

Lee felt a cold shiver run down his spine.  He was never going to get used to her. 

The video stopped and disappeared, leaving a bunch of files in it's place. When Lee opened a few of them, his eyes nearly bugged out of his head.

"There's not enough cells left at the precinct for this." He grinned.

She lived on a long stretch of empty road right off the highway. With so many rumors of it being haunted, she fit right in. It helped that she looked like the urban legend of a disappearing hitchhiker.
Rumor had it that if you picked up the ghostly hitchhiker, she'd disappear half-a kilometer down the road and crash the vehicle. More likely that the freaked out driver lost control of their cars or truck and fish-tailed into a ditch than the hitchhiker making them crash. It's not like they were harmed. Well... mostly unharmed.
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The thugs who were currently cursing at the empty security truck weren't so lucky one was already down. Hair turned white and hand-shaped welts around his neck. He was only unconscious. She din't need to kill him to feed. Not when there were so many lovely snacks. She dropped thug 1 in the driver's seat.

The other thugs slowly noticed that one of their own was missing when they heard the thud. All arguments stopped as they approached the front of the truck, guns out. Then the truck started moving, even if though with the engine off. The road was flat (no sign of an incline), so it couldn't be the handbrakes.
The truck stopped again. This time they reached the front doors and opened them from both sides. As one they peelef inside.

All of them were later found unconscious by Inspector Lee and his partner. Hair turned white and with hand-shaped welts around their neck.

She walked past them unseen. They were too busy trapped in their minds, their worst fears & terrors leaving them blind. A flick of the wrist sent the guard's keys flying to her.  Letting her unlock the door without damaging it and retrieve the shaken but unharmed little girl.

"It's alright. You're safe."  She whispered to the child without saying a word, picked her up and walked out. Leaving the little girl clutching her neck to wonder who this person was and why all the bad man were shaking & screaming. But she felt safe.

It was only later that the child would remember that the girl wore no shoes and left no footprints on the dusty, grimy floor.