Indonesian police arrested a former top official in the intelligence agency Wednesday on suspicion of involvement in the mid-air poisoning death of a top human rights activist in 2004.

The announcement is a major break in the probe into the killing of Munir Thalib and represents the first formal acknowledgment by authorities that the powerful State Intelligence Agency may have been involved.

Police spokesman Abubakar Nataprawira said Muchdi Purwoprandjono, a deputy head of the agency at the time of the murder, was arrested late Wednesday after voluntarily turning up for questioning.

He said Purwoprandjono had been declared a suspect in the murder, a formal step in criminal investigations here, which means police believe they have enough evidence to bring the case to trial.

Neither Purwoprandjono or his lawyers were immediately available for comment.

Earlier this year, the Supreme Court sentenced Pollycarpus Budihari Priyanto, a 46-year-old pilot for Garuda Indonesia, to 20 years in jail for his part in Thalib’s murder.

An independent fact-finding team established by President Susilo Bambang Yudhoyono revealed phone records showing calls between Priyanto and a phone registered to Purwoprandjono before the murder.

Purwoprandjono testified at Priyanto’s trial that someone borrowed his phone to make the calls.

Fellow rights activists and Thalib’s widow have long urged authorities to arrest Purwoprandjono.

The investigation into Thalib’s killing is seen as a test of how much Indonesia has changed since the days of Suharto, the dictator who ruled the country for 32 years until democracy riots forced him to resign in 1998.

State-sponsored killings were common during Suharto’s regime and military and police officers were largely above the law.

Thalib, 38, rose to prominence toward the end of Suharto’s regime. He went on to probe killings by Indonesian troops during East Timor’s bloody struggle for independence and military-led violence in the separatist provinces of Papua and Aceh.