(CNN) -- Investigators have narrowed their probe into the disappearance of Oregon boy Kyron Horman and will reassign some deputies involved in the search, the local sheriff said Wednesday, but he denied the effort was being "scaled back."
Multnomah County Sheriff Dan Staton said eight to 10 of his deputies will remain assigned to the case as part of a multi-agency task force. But with no sign of Kyron since early June, Staton said his department has to put some manpower that has been devoted to the search back onto the streets of his county, which includes Portland.
"We have taken critical hits in all of the units throughout the agency to support this investigation," he said.
Kyron, whose eighth birthday was last week, was last seen June 4. His stepmother, Terri Horman, said she dropped him off at school on the morning of June 4.
Terri Horman has been the subject of intense scrutiny for several months. In divorce filings, her ex-husband, Kaine Horman, said he believes that Terri Horman "is involved" in the boy's disappearance, but no arrests have been made.
Staton said investigators have ruled out enough possibilities to give the probe a tighter focus with fewer people, and he disputed any characterization that the investigation was being "scaled back" or relegated to "cold case" status.
Without disclosing details, Staton said the case was advancing "in a very successful fashion" that will allow him to return deputies to their normal duties.
"I think there will be things coming out of this investigation that will surprise you," he told reporters, adding, "We have knowledge of things we wish we didn't."
But Staton said his department has spent more than $1 million on the effort so far.
"We've reached the point where if we don't go to a task-force model, this is going to critically affect the services we provide to the community," he said.