Kopp, a fugitive, has until now been described only as a material witness and a nationwide warrant had been issued so that he could be held for questioning. There was no official confirmation of the decision to upgrade the warrant, but Denise O'Donnell, the U.S. attorney for the Western District of New York in Buffalo, has scheduled a news conference Thursday to (announce) a  major development  in the Slepian murder investigation.  
 Verb: announce
Yes