Family members of a petitioner who died in the custody of "interceptors" after traveling to the Chinese capital to pursue a complaint against the government have questioned official claims that he had a heart attack. Liu Zhen died last week after being held for more than two months a police-run detention center in Liaoning's provincial capital Shenyang in northeastern China, his home city. He had been detained after setting out to lodge a petition at the U.S. embassy in Beijing last October, around with a dozen other people. He was detained and taken back to Shenyang by "interceptors," before being held under criminal detention in the city's Hunnan district before his formal arrest in December. His family was informed on Jan. 13 of his death from a "heart attack," but relatives who identified his body said there were visible marks of injury to his chest area that led them to distrust the officially registered cause of death. "Liaoning rights activist Zhu Zhongxiao told RFA that Liu's grown son is now incommunicado after being called in by police for "a chat." "His son had been planning to meet with some rights defenders in Shenyang[on Tuesday]," Zhu said. "But he was taken away by police, and we don't know if he even went willingly; it's likely that he now has restrictions on his freedom." He said Liu's son had been detained after he posted on the Sina Weibo social media platform about his father's death. "His son posted to Weibo that there were greenish-purple marks on his father's chest, which the authorities said were caused by their attempts to resuscitate him," Zhu said. "If that's so, then why wouldn't they allow the family to take photos?" He said the family had submitted a request for an autopsy to the local prosecutor's office on Monday, but that they have no idea where Liu's body is being held. "Where has the body gone?" Zhu said. "That is one question mark." "A long and slow process' Li Ning, whose mother Li Shulian's death in custody in 2009 led to the charging of six officials with "illegal detention" last month, said the remains of a loved one are the only evidence remaining for families who suspect foul play after a death in custody. "The family has the right to apply for an autopsy, and if they are suspicious about the official autopsy, they can apply for an autopsy carried out by a third party," Li said. "They can't stop you taking photos of the body, and the family also has the right hold the detention center to account and to hire a lawyer to represent them." "They can also demand access to relevant video and audio recordings," she said. But she said any attempt to see justice done isn't for the faint-hearted. "This is a long and slow process, and a very, very tough one," Li said. "There are some similarities between[Liu's death] and my mother's case, and it took me 10 years to get to this point because the family didn't have possession of the body." "It is very, very hard to take this through official channels," she said. Last month, authorities in the central province of Henan executed a petitioner for killing a police officer who was forcibly escorting him home from a petitioning trip in the Chinese capital. Veteran activist Xu Youchen, 58, was executed on Nov. 15 after the China Supreme People's Court approved his death sentence the month before, according to London-based rights group Amnesty International, which had campaigned for a reprieve. But rights groups have also cited procedural irregularities with the handling of the policeman's death. Authorities cremated the body of the policeman allegedly killed by the couple just four days after he died, making it impossible to re-examine the exact time and cause of death, Amnesty International reported. China's army of petitioners, who flood the ruling Chinese Communist Party's official complaints departments with more than 20,000 complaints daily across the country, frequently report being held in "black jails," beaten, or otherwise harassed, if they persist in a complaint beyond its initial rejection at the local level. They are often escorted home forcibly by "interceptors" sent by their local governments to prevent negative reports from reaching the ears of higher authorities.