This quote makes me think he was awake at the time Christina and walker left the apartment to walk to the garage:
Steven Nickerson was with Morris before she went missing and said she seemed a little upset that night, but he didn't know what was wrong. He said she insisted on driving back home to Fort Worth, but he never realized it would be the last time he saw her before she was reported missing.
"She was loved by everyone. She was the nicest person I've ever met, great personality," said Nickerson. "I don't see anyone that could lay a finger on her."
http://www.nbcdfw.com/news/local/Search-Efforts-Continue-for-Missing-Fort-Worth-Woman-274404321.html
Then there's this quote who omits SN altogether and focuses only on the walker:
Investigators say Morris went to a tavern and then to a friend's apartment before she was spotted on surveillance footage at 3:57 a.m. entering a parking garage with a man her family says Morris has known since high school.
Cops say they have questioned that friend and he has not been named a suspect.
http://www.hlntv.com/article/2014/09/19/search-continues-missing-woman-christina-morris