Tanya Zuvers' ex-husband, John Skelton, is serving a prison term for kidnapping and has refused to say where the boys are or if they are alive, the Detroit News reported.
"As their mom, I still have that hope that they're still alive, but I know the reality is it's very possible they're not," she told the newspaper. "We're still looking for the clues, but my reality is there's a very good possibility my sons are no longer alive on this Earth. It took me a long time to come to that realization."
Zuvers, 47, lives in Morenci, a small town about 75 miles southwest of Detroit and just north of the Ohio line. She reported her sons missing when Skelton, 42, failed to return them in November 2010.
If they are still alive, Andrew is 12, Alexander 10 and Tanner 8.
Skelton, who had previously taken the boys to Florida without permission, told police they were with a couple he had met via the Internet. He later claimed they were with an underground network of child-protection activists.
Investigators discovered Skelton had traveled to Holiday City, Ohio, about 25 miles from Morenci, on the day after Thanksgiving in 2010. They also found he had done searches on line for information on how to break necks.
Skelton pleaded no contest to kidnapping charges and was sentenced to 10 to 15 years. Zuvers said she occasionally emails him, asking him to reveal what he did with his sons but has yet to hear back.
Notable deaths of 2014 [PHOTOS]