A statement that a 21-year-old Great Falls man made to police in March, describing how he stabbed his mother to death, cannot be used against him, a Fairfax County judge has ruled, because detectives started their interrogation with this question: "Do you know why we're here?" That inquiry, by Fairfax homicide Detective David W. Allen, elicited this answer from Jayant Kadian: "Yeah, because I stabbed my mom in the neck." Fairfax Circuit Court Judge Kathleen H. MacKay ruled last week that Kadian should have first been told of his rights to remain silent and have an attorney present. The detective's...