Mona Reeder/Dallas Morning News, via Associated Press  A vigil was held in Grapevine, Tex., for members of a family killed on Christmas Day; mostly static and breathing were heard on a 911 call in the case.  “Grapevine 911, where is your emergency?” she asked.  “Hello, Grapevine 911?” the dispatcher said.  The caller responded with two deep breaths. Days later, using audio software to scrutinize a recording of the call, investigators would find hints of the horror unfolding on the other end of the line. But at the moment, the dispatcher faced the signature predicament of her corner of law enforcement: an open line.  “Afterwards, when you realize, ‘I was listening to something horrific and I couldn’t do anything,’ that’s when the emotions kick in,” said Gary Allen, a retired dispatcher who worked for 20 years in Berkeley, Calif. “When you find out what you were in the middle of over the phone.”  Open-line calls have long plagued emergency dispatchers, who handle about 240 million calls in more than 6,000 communications centers across the country, according to Trey Forgety, government affairs director for the National Emergency Number Association, a trade group. The advent of cellular technology has only expanded the potential for confusion. To those on the receiving end of the line, the silence can signify a prank, a pocket-dial or, just as easily, something haunting.  Even in the land-line age, open-line calls provided a singular vexation. On New Year’s Day in 1989, Sharyn Gilbert, a dispatcher for the Los Angeles Police Department, handled a 3:58 a.m. call from the home of O. J. Simpson. Six years later, she became the opening witness at his murder trial, called by prosecutors to establish a history of violent behavior.  “O.K. So the call came to you, right?” asked an assistant district attorney, Christopher Darden, according to a transcript.  “Right,” Ms. Gilbert said. “It was an open line.”  “O.K. Could you hear anything over the open line?” Mr. Darden asked.  “No,” Ms. Gilbert answered. “At the beginning, no.”  After a period of silence, Ms. Gilbert testified, she eventually heard “a female screaming, and that’s when I went back and changed my incident type from ‘unknown trouble’ to ‘a screaming woman.’ ”  Then, Ms. Gilbert testified, “I heard someone being hit.”  On cross-examination, the defense lawyer Johnnie L. Cochran Jr. challenged her claim.  “You hadn’t talked to anybody, so you don’t know what was taking place at that location, do you?” Mr. Cochran asked.  “No, I do not,” Ms. Gilbert said.  “You have no way of knowing that, do you?”  Ms. Gilbert said, “Only what I heard.”  Modern dispatchers work under banks of video screens, answering calls with a mouse click, speaking into headsets and monitoring digital mapping programs. About 70 percent of their calls come from cellular phones, which tend to provide only a vague indication of the caller’s whereabouts, according to the Federal Communications Commission.  “Cellular changed everything enormously,” Mr. Allen said. “You didn’t have any idea where it was coming from. People could sit on the phones and dial accidentally. There were a lot of misunderstanding calls, finding out a day later that there was an emergency out there. Even if you heard something on the phone, you didn’t know where to go.”  Across the country, policies on open-line calls vary, depending on the size and resources of the city. Some require dispatchers to investigate every call, reaching out to cellphone service providers for more information if necessary. The results can be unpredictable. In 2004, the New Jersey Supreme Court ruled that an open-line call had not provided proper grounds for a search that turned up marijuana plants, grow lights and an elaborate watering system.  Faced with the uncertainty of an open line, dispatchers sometimes send officers into comically innocuous settings, some of which make the local newspapers. In 2008, when a dispatcher in Shrewsbury, Mass., heard a child screaming in the background, the responding officer reported that an “8-year-old child was given a timeout and called 911.” And last winter, a dispatcher in Glenburn, Me., sent a deputy to an empty house, where a pug named Lucy was found chewing on the phone that had dialed 911.
Open-line calls in which no one speaks are perplexing to 911 dispatchers, as in a recent case in Texas in which the fatal shooting of a family was unfolding.