( 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 did n'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 do n't go to a task-force model , this is going to critically affect the services we provide to the community , '' he said .
Sheriff wants a task force to take up Kyron Horman probe . The sheriff says he has been told by the FBI that it is looking into whether there was any wrongdoing in his department. More than $ 1 million has been spent on the case so far , he says .