ST JOHNS, MI  — Eighteen months ago, police in St. Johns arrived at a small upstairs apartment to check on a fourth-grader who hadn’t been seen in weeks. They made an unthinkable discovery.

Her decaying corpse was found in bed beneath a layer of blankets, her body naked but for a pair of socks and a urine-soaked T-shirt between her legs. The quest to figure out what happened to her would haunt school officials, baffle investigators and leave a painful scar on a small community that hugs its kids — even the ones it barely knows.

This is Vienna Parker’s story.

Part One: 'I know she's dead.'

Part Two: 'She said she'd be OK'

Part Three: 'I never worried that she was in danger'

Part Four: 'I have to live with the guilt ...'