The police chief in Nashua said that detectives investigating the stabbing deaths of an elderly couple last month have a ‘‘very good handle’’ on the case and that getting it resolved is the department’s top priority. Police Chief John Seusing told The Telegraph that the department is focused on catching the killer or killers. No one has been arrested. A home health worker discovered the bodies of William and Eleanor Grant stabbed to death inside their home on June 17. Since then, authorities have released no information, other than that the deaths were homicides by stabbing.