Otherwise, the disappearance of Engel - probably the most high-profile international television reporter on a U.S. network - would have been big news.
Engel and three colleagues, producers Ghazi Balkiz and Aziz Akyavas and photographer John Kooistra, escaped during a firefight between rebels and their captors, forces sympathetic to the Syrian government. The journalists were dragged from their cars, kept bound and blindfolded and threatened with death.
NBC said it did not know what had happened to the men until after their escape. The first sign of trouble came last Thursday, when Engel did not check back with his office at an agreed-upon time.
The Associated Press learned of Engel's disappearance independently and was asked to keep the news quiet upon contacting NBC, said John Daniszewski, the AP's vice president and senior managing editor.
"A general principle of our reporting is that we don't want to write stories that are going to endanger the lives of the people that we are writing about," Daniszewski said. The first few days after an abduction are often crucial to securing the captive's release.
In any case, he said, the AP never had enough information to report to its standards. "The fragmentary information we did receive was not solid or sourced in a way we could use. We had no actual news to report until they got out on Tuesday and NBC went public with the story," he said.
CBS News also said that it had honored NBC's request, but a spokeswoman declined to discuss it. ABC, Fox News and CNN were also contacted by NBC.
CNN, in an editor's note affixed to a website story on Engel's escape, noted NBC's request. CNN said it complied to allow fact-finding and negotiations to free the captors before it became a worldwide story.
"Hostage negotiators say that once the global spotlight is on the missing, the hostages' value soars, making it much harder to negotiate their freedom," CNN said.
For similar reasons, the AP did not report its own news several years ago when a photographer was kidnapped in the Gaza Strip, securing his release within a day. In one celebrated case of secrecy, The New York Times withheld news that reporter David Rohde was kidnapped while trying to make contact with a Taliban commander in Afghanistan. Rohde escaped after seven months in captivity.
It wasn't clear whether Engel's abductors knew what they had at the time. That knowledge, CNN argued, could have greatly complicated any negotiations. In this case, the captors did not make any ransom demands during the time he was missing.
This isn't simply a professional courtesy; the AP has withheld news involving overseas contractors in the past, Daniszewski said. For similar reasons, the organization does not reveal details of military or police actions it learns about beforehand if the news will put people at risk, and doesn't write about leaders heading into war zones until they are safely there.
Still, it's not a decision lightly taken by news organizations. "The obligation of journalists is to report information, not withhold it, except in exceptional circumstances," said Robert Steele, a journalism ethics professor at DePauw University.
The news that Engel was missing was first reported Monday by Turkish journalists who had heard about Akyavas' involvement, and was picked up by the U.S. website Gawker.com. In explaining why the news was reported, Gawker's John Cook wrote that no one had told him of a specific or even general threat to Engel's safety.
"I would not have written a post if someone had told me that there was a reasonable or even remote suspicion that anything specific would happen if I wrote the post," Cook wrote.
He also noted that China's Xinhua News Agency and the Breitbart website had also reported on Engel's disappearance. Breitbart's John Nolte attached a note to his report saying that he wasn't even aware of any news embargo until after hearing that Engel had been released.
The news was also tweeted by a small number of journalists, apparently unaware of the embargo request.
Whether a disappearance has become widely known could influence a decision by AP on whether to withhold the news, Daniszewski said. In this case, it wasn't clear that it had been widely circulated, he said.