Missing Ancestor in Chicago!

Picture of Olai E. Stillufsen
My Great-Grand-Father vanished in Chicago 100 years ago.
My grand-grandfather (Olai Emanuel Stillufsen, b: 1956, Vanse, Norway) left wife and three children in Norway and moved to Chicago. There he worked as a kind of woodworker.
What happened after he left Norway the last time in 1896 is unknown to us but
all my family is keen to find out more.
He did at least one trip back to Norway and the last return to Chicago was on April 10th, 1896 from Kristiansand, Norway to destination Chicago, USA.
In the shipping list his surname is listed as 'Silufsen', which is a typing error of 'Stillufsen'.
My Grandfather was then 6 years old and this was the last time he saw him.
The Norwegian census of 1900 is showing his spouse as "widow ".
My Grandfather did not want to talk about his father and how he vanished.
The way my grandfather reacted to any questions about Olai indicated that "something had happened" and all I can suggest is that he might have remarried in USA.

If there is anyone who can help me I will be very appreciated.