Sean Michael Phillips, 23, appeared at his arraignment in Mason County by video link from the Carson City Correctional Facility, the Muskegon Chronicle reported. He was convicted last year of falsely imprisoning 4-month-old Katherine Phillips and sentenced to 15 to 20 years.
"New evidence has been discovered which supports a murder charge in this case," Michigan Attorney General Bill Schuette said at a news conference in Mason County.
Schuette and Mason County Prosecutor Paul Spaniola did not give any details.
Katherine, who has become known as "Baby Kate," was last seen on June 29, 2011. A letter allegedly written by Phillips last year to the baby's mother, Ariel Courtland, said the death was accidental and the baby was in "a peaceful place."
This June, volunteers searched wooded areas, trying to find combinations of plants and soil that matched material found on Phillips' shoes.
Courtland and members of her family attended the news conference, although she did not speak to reporters. Mason County is a rural area on the Lake Michigan shore of the lower peninsula.
"It's been a long time coming. I'm glad they're going to charge him with murder, because that's what he did," Courtland's grandmother, Linda Carlson, said.