MANILA, Philippines - Feared and loathed by his enemies, Andal Ampatuan Jr. is the heir apparent of a powerful Muslim clan in the southern Philippines whose family history is written in blood.

The chubby, stone-faced man in his 40s with a penchant for expensive guns, is the son and namesake of Andal Ampatuan Sr., the clan patriarch who has ruled Maguindanao province for almost a decade.

Ampatuan Jr. went on trial accused of multiple murder on Wednesday over the November 2009 massacre of 57 people.

The victims, which included 30 journalists, were shot dead and dumped in mass graves apparently to end a political challenge from a rival clan.

The defendant, who witnesses claim was among the gunmen, denies a role in the killings.

Five other Ampatuans, including Andal Snr, have been detained and are among 196 people charged for their alleged involvement in the massacre.

Ampatuan and his father have long had reputations for using fear and violence to stifle opponents and expand their power, according to human rights monitors and others who have knowledge of the family.

But nearly a year after the killings, more than half of those charged remain at large.

Five other people linked to the Ampatuans, including a former employee who agreed to testify against the clan, have since been murdered, according to Human Rights Watch.

The New York-based group alleges the clan leaders, who have been detained, continue to give orders to their armed supporters from behind bars.

"Abuses in Maguindanao have not stopped with the arrest of six members of the Ampatuan family," Elaine Pearson, Human Rights Watch's deputy Asia chief, said in a statement Wednesday.

"Prompt investigation of ongoing crimes is essential to prevent further killing and to stop suspects from interfering with the trial."

Ampatuan Sr. and his clan controlled Maguindanao with brutal efficiency over the past decade under the patronage of then President Gloria Arroyo. The clan leader was governor and his sons and other relatives were town mayors.

Arroyo is accused of turning a blind eye to their excesses in exchange for using the Ampatuan's vast private army as a proxy force against Muslim separatists and its influence to win votes in the troubled region for her political allies.

As a bulwark against a decades-old separatist rebellion that has claimed 150,000 lives, the Ampatuans were given a lot of leeway, said Julkipli Wadi, an Islamic studies scholar at the University of the Philippines.

"They shared power amongst themselves, ruling with an iron fist in Maguindanao backed up by their huge armory," Wadi told AFP.

"The Ampatuans are the political warlords in the area. Any attempt at politics by a rival family they consider as threat to their rule is violently cut short," he said.

Ampatuan Jr. had a Maguindanao town created in his nickname, Datu Unsay, by a Muslim regional autonomous government led by an older brother. Their father groomed the favorite son and namesake as his successor as provincial governor.

Ampatuan Jr., then the mayor of Datu Unsay town, allegedly led the massacre to stop the rival from running against him for the post of Maguindanao governor in last May's national elections. The rival, Esmael Mangudadatu, won the election.

The clan rose to political prominence when Andal Ampatuan Sr. was named officer-in-charge of the province after a strongman president Ferdinand Marcos was toppled in 1986, Wadi said.

He eventually was elected governor of the province in 2001, and has since consolidated his grip on power by stockpiling arms and co-opting government militiamen deputized to fight against insurgent groups.