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Mary Grace Morales is still waiting for justice 18 months after her reporter husband and sister were gunned down in a massacre of 57 political opponents and journalists in the Philippines — the world's single worst mass killing of media workers.

"I don't understand why it's so slow," Morales said in a telephone interview Wednesday from the southern Philippines. "Why does the trial take so long?"

Even once the court process is completed, there is no guarantee justice will be served, the Committee to Protect Journalists said Wednesday in its annual report on impunity in journalist killings worldwide.

"Entrenched corruption and dysfunction in law enforcement has thwarted justice in journalist murders," the committee said in its 2011 Impunity Index spotlighting countries where journalists are slain and killers go free.

"Suspects have been publicly identified in dozens of unsolved cases examined by CPJ for this index, but authorities have been unable or unwilling to gain convictions," it said.

Morales said her husband, Rossel, 35, and her sister Marites Cablitas, 39, were both newspaper reporters keen to cover an electoral convoy in the southern province of Maguindanao in November 2009. Rossel Morales had originally worked as a disc jockey at a radio station, but his sister-in-law convinced him that reporting the news was more fun.

"We knew that it was a dangerous job, but what else could I do?" said Mary Grace Morales. "They both really wanted to keep working as journalists."

The two reporters were among at least 32 journalists killed in the brazen attack by as many as 150 gunmen on a caravan of a candidate's family and supporters and the media workers trailing behind. The massacre exposed the power and impunity some clans still enjoy in impoverished, isolated areas of the Philippines.

"That day, I heard my sister's name on the radio, but at first I didn't hear my husband's," Morales said, recalling the terror of learning about the mass killings. "Finally, one of my neighbors heard his name and I knew that yes, he too, had died."

The couple had three daughters, now 11, 10 and 8 years old.

The region's powerful clan patriarch Andal Ampatuan Sr. pleaded not guilty in Manila on Wednesday to charges he masterminded the attacks.

The main suspect in the killings is his son, former Mayor Andal Ampatuan Jr., who is accused of ambushing the election convoy of his political rival. The Ampatuans held key posts in an autonomous Muslim region in the country's south.

The annual update of the Impunity Index showed that vast majority of murdered journalists are local reporters, like Morales' husband and sister. Only 6 percent of unsolved cases on the index involve international journalists.

It also found that prior threats against a journalist can be a powerful predictor of future violence. More than 40 percent of the victims counted by the index had received prior threats.

For this latest index, CPJ examined journalist murders that occurred between January 1, 2001 through December 31, 2010, and that remain unsolved. Only the 13 nations with five or more unsolved cases are included on the index. Cases are considered unsolved when no convictions have been obtained.

In descending order, ranked by the number of unsolved journalist murders per 1 million inhabitants, the 13 countries are:

— Iraq. With a rating far worse than anywhere else in the world at least 92 journalists have been murdered in the past decade, with no convictions. Among the four murder victims in 2010 was Sardasht Osman, a contributor to several news outlets who received threats for coverage accusing Kurdistan Regional Government officials of corruption.

— Somalia. 10 murders are unsolved, including the shooting of a senior journalist for state radio in 2010.

— Philippines. The murders of at least 56 journalists remain unsolved, included the 32 slain in Maguindanao.

— Sri Lanka. At least nine killings are unsolved, including the 2009 murder of Lasantha Wickramatunga, a leading editor and government critic beaten to death by motorcycle-riding assailants.

— Colombia. Historically among the most murderous places for journalists, it has shown improvement as authorities successfully prosecute some killings. But 11 killings from the past decade remain unsolved.

— Afghanistan. Seven unsolved killings include the 2008 murder of a reporter for BBC's Pashto service.

— Nepal. Six journalist slayings are unresolved, including several believed to have been committed by Maoist rebels.

— Mexico. The country's impunity rating worsened for the third consecutive year, with at least 13 journalist murders unsolved amid widespread drug-related corruption. Photographer Luis Carlos Santiago of the Ciudad Juarez newspaper El Diario was among those killed last year, gunned down in a shopping center parking lot on a weekday afternoon.

— Russia. The cases remain open on the murders of 16 journalists who reported on official corruption, organized crime and unrest in the North Caucus, including the contract killings of investigative reporters Anna Politkovskaya and Paul Klebnikov, and the mysterious poisoning of a newspaper editor.

— Pakistan. At least 14 journalist murders have gone unsolved over the past decade. The victims include a veteran reporter who was shot multiple times in 2010 as he entered the press club building in a volatile town near the Afghan border.

— Bangladesh. The murders of five print reporters who covered local corruption and crime stories.

— Brazil. Five unsolved killings.

— India. Seven unsolved cases, including that of a reporter murdered in 2006 after writing about corruption in the forestry service.