<p>An angry letter found tacked to a tree behind a restaurant where the sniper wounded a man this weekend complained of six failed attempts to reach police, and threatened more killings, of children in particular, if millions of dollars were not deposited in a bank account within two days, law enforcement sources said.</p>
<p>The letter listed half a dozen calls that had been "ignored" by operators answering phones at the command center in Rockville, Md., the Montgomery County police station and the FBI. It even named some of the people who had answered the phones.</p>