By Lisa Richwine
April 19 (Reuters) - Cable news channel CNN saw a big spike in ratings as viewers kept tuned to its coverage of the Boston Marathon bombing, even after an embarrassing mistake in which it claimed a suspect was taken into custody earlier in the week.
Viewership on Time Warner-owned CNN nearly doubled from the previous week, from the first news of the bombings that killed three people at the race's finish line to the start of a manhunt for two suspects.
CNN's Monday-to-Thursday audience jumped by 194 percent, according to Nielsen data provided by Horizon Media, to an average of 1 million viewers throughout an entire day.
That enabled CNN to leap over Comcast Corp's MSNBC, which had led CNN by an average of 18,000 viewers before the bombings. Both trailed ratings leader News Corp's Fox News Channel, whose audience increased by 48 percent to an average of 1.6 million viewers.
"CNN, despite its ratings woes, is still a destination network for the light and casual news viewers," said Horizon Media analyst Brad Adgate. "They have been around longer than anyone else."
On Wednesday, CNN made a major mistake when it wrongly reported that authorities had a bombing suspect in custody. A CNN spokeswoman said the information was based on three credible sources and was changed as soon as sources provided new information.
The error was skewered by social media comments and comedian Jon Stewart on the "Daily Show."
Despite the criticism, CNN's ratings increased by about 263,000 viewers from Wednesday to Thursday. On Thursday, when law enforcement officials released photos and videos of the two suspects, CNN's audience averaged 1.2 million people.
"CNN is everyone's whipping boy," said Rick Edmonds, media business analyst at the Poynter Institute. "They took quite a drubbing from Jon Stewart. That mistake is only really important to those of us who cover the media. CNN still has a pretty strong reputation when it comes to the news."
Crisis coverage typically boosts networks. The Boston bombing turned into a multiday drama still playing out with a suspect on the loose, said Roberto Suro, professor of journalism at the University of Southern California's Annenberg School.
"It's a great TV story," he said. "The image of seeing a fabled American city in the midst of this huge paramilitary operation is just really gripping."
But the viewership bump is typically short-lived, evaporating as soon as the drama ends. "When news recedes, the viewership drops," he said. "This will end sooner or later and people will go back to their old news-viewing habits."
With one suspect still at large, U.S. broadcast networks ramped up their schedule with added programs while police continued searching for one of the two bombing suspects.
The networks shifted between their usual daytime coverage and broke in with specials that sometimes lasted a half hour or more. ABC, NBC and CBS scheduled specials for Friday night.
Comcast's NBC is set to air a one-hour "Rock Center with Brian Williams" from Boston. NBC also said it would broadcast its "Weekend Today" show with hosts Lester Holt and Erica Hill from the city.
Walt Disney Co's ABC sent "20/20" host Elizabeth Vargas to Boston to anchor a one-hour special, and will broadcast its late night news program "Nightline" from Boston.
CBS Corp, which broke away during the day for special reports with prime time anchor Scott Pelley, said it would extend its 6:30 p.m. "Evening News with Scott Pelley" to an hour and added a one-hour special, "CBS News Special Report: Boston Bombers."