A large-scale manhunt is underway for a serial killer in Chongqing, following the latest killing during an armed robbery on Friday which left a woman dead. The military has reportedly been called in to help authorities hunt the 42-year-old suspect, who is believed to have killed nine people across Chongqing, Changsha and Nanjing.

Reinforced police forces were deployed on Sunday to take part in a citywide search for Zhou Kehua, who has been identified by police as the suspect in a series of armed robberies and killings. The search was centered around Gele Mountain, where he was believed to have been hiding.

Army forces in the southwest municipality have also joined the hunt, as the suspect, who remains on the Ministry of Public Security's wanted list, is still at large, the Shanghai-based Oriental Morning Post reported.

According to media reports, police found a ragged dark-green T-shirt, two cigarette boxes, peeled wires and leavings in a cave in the mountain.

Song Yang, a Chongqing resident who visited the mountain on Sunday, told the Global Times that "a group of police officers could be seen about every 100 meters," adding that vehicles were also being carefully inspected.

Police from neighboring provinces are also getting involved in the operation. Changsha, in Central China's Hunan Province, has deployed police to Chongqing and stepped up inspections at traffic checkpoints since Saturday. Hubei Province authorities have also been on alert.

Zhou, from Ertang village in Chongqing's Shapingba area, shot a woman in front of a Bank of China branch in that district on Friday, before grabbing her handbag which contained about 250,000 yuan ($39,300) in cash, then escaped on a motorized tricycle. The woman died on the spot and two others were injured.

The man then killed a railway police officer called Zhou Yanchao on Saturday afternoon, while being questioned by Zhou during his getaway, according to media reports.

The Chongqing Municipal Public Security bureau had no updated information relating to the case on Sunday.

"We will release the latest information on our website as arranged by the ministry of public security," said the female officer, who declined to give her name.

The Chongqing police are offering 500,000 yuan ($78,600) to anyone who provides information leading to his arrest, while Changsha has offered a reward of 300,000 yuan.

Zhou is suspected of committing several murders - apparently in order to steal large sums of cash - in several cities along the Yangtze river since 2004, including one robbery outside a bank in Nanjing on January 6, according to police.

He was at home on January 19, just 13 days after the Nanjing killing, his mother Chen Shizhen told the Beijing Times newspaper.

A criminologist, who requested anonymity, said that tracking down the suspect has been difficult because as his family and local villagers attest, he has an antisocial personality. This has made it harder to collect clues.

"He acted on his own every time, making the collection of clues even more difficult," he said, adding that Zhou's elaborately planned schemes and determined nature are also important factors impeding the manhunt.

Meanwhile, the futile attempts by police to catch him have sparked speculation that Zhou may have had a military background, giving him skills that have proved useful in evading capture.

But his mother has denied these allegations, insisting that Zhou was rejected by the army due to a blood pressure problem, according to a report in the Beijng Times.

Mao Lixin, an associate professor of criminal law science at Beijing Normal University, said that even though uncertainty surrounding the suspect has caused obstructions to the case, it has also been a reflection of police inefficiency to a certain extent.

"The police need to improve their capabilities in arresting suspects in emergency situations," Mao told the Global Times.

Related report:

Suspected killer remains at large after attempted robbery in Chongqing

A suspected serial killer who allegedly committed an armed robbery that left one person dead and two injured in Southwest China's Chongqing Municipality on Friday morning remains at large despite a citywide police manhunt by local police.