The masterminds of the Philippines' worst political massacre were found guilty Thursday of murdering 57 people, a rare conviction of powerful personalities in a country notorious for its culture of impunity.

Officials said the gunmen slaughtered 58 people a decade ago and dumped their bodies in pits as part of a mass killing, though only 57 bodies were recovered.

Leaders of the Ampatuan family, a powerful political dynasty, had been accused of orchestrating the killings in a bid to quash an election challenge from a rival clan.

Some 32 journalists were among those murdered on November 23, 2009, making the massacre also one of the worst ever of media workers.

A Manila court on Thursday found 43 people guilty as principals or accessories to 57 murders led by Andal Ampatuan Jnr, who had been planning to run for provincial governor against the rival.

As principal suspects, Ampatuan and 27 others - including seven of his relatives - were each sentenced to 30 years in jail without parole, the court ruling read.

Fourteen members of the local police and a member of the Ampatuan family's armed militia force were sentenced to between eight and 10 years in prison as accessories.

Two clan leaders and more than 50 others - mostly police officers and alleged members of the Ampatuan militia - were acquitted either on "reasonable doubt" or the prosecution's failure to prove their guilt. The judge also dismissed the charges over the 58th victim whose body was not found save for his dentures.