Here is the case of a missing paragraph that turned into a trap door that dropped a man into prison.

The paragraph vanished from a police report in a Brooklyn criminal case, but essential information has been hidden from people accused of crimes in courthouses across the country. Even though failing to share exculpatory information is among the most serious breaches of ethics and law for the police and prosecutors, there is little personal or institutional accountability for such tactics.

In 2010, to convict a man named Wayne Martin of killing two people during a stickup of a Brooklyn tire repair shop, someone in law enforcement went to the trouble of blanking out a paragraph in a homicide report.

The erased portion said that a witness had identified someone other than Mr. Martin as the gunman.

In still another report, another witness also told detectives that it was not Mr. Martin who had done the shooting.