A serial killer who goes by "The Mask."
His greatest strength is
his powers of observation. He stalks someone for a year, then on New
Year's Eve he murders them and hides the body. He then impersonates his
victim for the next year (or until he gets bored living their life) all
the while stalking his next kill. When he moves on, his last victim's
family and friends find out about the murder- a year after it happened.
As a younger man he made a lot of mistakes, so he thinks that doing
this gives him second chances at life.
[credit:] swordtech @ NaNoWriMo