Neighbors told ABC News they routinely saw Hoffman in the park, a former gravel quarry with wooded areas and deep fishing ponds, early in the morning, sometimes carrying a backpack.
Hoffman was convicted of arson in 2001, for setting fire to a condominium complex in Steamboat Springs following a robbery. He pleaded guilty to first degree arson, theft and burglary and served eight years in prison.
Sarah and the others disappeared last Wednesday. Tina Herrmann was reported missing when she did not show up to work at a Dairy Queen. When police searched the family home Thursday they found it littered with beer cans, and splattered with a large amount of blood.
Neighbors near Hoffman's home described the man's behavior as "bizarre" and "weird." Hoffman moved into the 2-level home last year. Until recently, he lived in the home with a girlfriend and her 8-year-old son.
Neighbors said Hoffman routinely climbed trees spying on them from his perch and would regularly, in both summer and winter, build fires.
"He was kind of weird he was always climbing the trees and stuff like that," said neighbor Ron Fowler.
Dawna Davis, 35, who lives next door to him, told The Associated Press that she told her children to stay indoors when he was out.
"He would sit and listen to us up in a tree. He had a hammock and he would sit there and listen to us," she said. "He was just different. He was very different."