As Chinese nationals Zhang Fulin and his wife were making supper at their home in the Vietnamese city of Mong Cai on March 27, they heard police shouting their names in Putonghua. It was at that moment they knew they could no longer flee the charges they were facing, which stemmed from an illegal banking operation in Wenzhou, Zhejiang Province.

Zhang, 46, the former chairman of the Wenzhou Mincheng Financing Guarantee Company, had amassed a fortune from friends and relatives with the promise of repayments with large quantities of interest.

When he was hit by liquidity problems during the city's private lending crisis in 2011, Zhang knew he would be caught for the crime of illegally collecting public savings.

Having amassed 100 million yuan ($16.12 million) in debt, and fearing the inevitable lawsuits that would follow, Zhang fled to Vietnam by boat and his wife followed him in January this year.

The couple rarely left their shabby rental house during their two months together on the run in Vietnam. Zhang had to change his phone number more than 20 times and his wife dissolved into tears almost every day due to the fear of being caught - a fear which proved to be valid.

The arrest was made after a two-month joint investigation between police in the border cities of Dongxing, in the Guangxi Zhuang Autonomous Region and Mong Cai, Vietnam. Wenzhou police assisted in the investigation.

It was the latest example of cross-border police cooperation, which has accelerated in recent years, particularly in relation to economic crimes.

The Ministry of the Public Security stated that in 2012, they arrested and brought back 331 suspects from abroad and transferred some 25 foreign fugitives to other countries, the Xinhua News Agency reported in February 2013.

Transnational hide-and-seek

Tracking down suspects abroad is a difficult task for Chinese authorities, as it is essential for multiple departments and judicial organs in China and overseas to share and verify evidence, a Guangxi police official surnamed Chen, who has been involved in arresting and hunting fugitive suspects in Vietnam, told the Global Times.

Chen said that sometimes the evidence which was verified by Chinese police could be rejected by Vietnamese police. In those cases, the police might need to do more investigation, slowing the process.

A scholar, surnamed Wu, from the People's Public Security University of China who specializes in cross-border police cooperation, told the Global Times that the process made some suspects think it was possible to evade charges by fleeing abroad.

Chen did, however, point out that due to the increasing cooperation between China and other countries, the trust between the different judicial organs was increasing, and in some cases, the process of tracking and arresting suspects was becoming more efficient.

Over the past 30 years, China has signed 33 bilateral extradition treaties and 47 criminal judicial assistance treaties with other countries, as well as set up police cooperation programs with over 150 countries and regions, the Legal Daily reported in 2012.

"Without those treaties, other countries could refuse to transfer suspects back to China due to differing geographical jurisdictions, according to international conventions. The treaties effectively mean it becomes the countries' duty to send those suspects back to their original countries," Wu said.

Wu added that most of those countries who signed treaties with China have borders with China or have a close trade relationship, such as Vietnam. But other Western countries, such as Canada and America, which are popular destinations for Chinese fugitives who commit economic crimes, don't have effective treaties with China.

Different systems 

Experts said that differences in judicial and political systems were stumbling blocks to extradition and prisoner transfers between China and other countries.

China's penalties under criminal law, particularly the death penalty, pose problems when transferring suspects, Liu Renwen, director of the criminal law research center under the Institute of Law of the Chinese Academy of Social Sciences, told the Global Times. Wu echoed Liu's opinion, pointing out that banning the extradition of prisoners who may face the death penalty is a common convention internationally.

Liu suggested that China should remove the death penalty for all non-violent crimes, including economic crimes, in order to facilitate the return of suspects who have fled abroad, and promote cooperation.

In 2011, China reduced the number of crimes that warranted the death penalty from 68 to 55.

Experts cited Lai Changxing's case as an example of death penalty disagreements. Lai, who made billions in the 1990s via fraud and smuggling schemes, was portrayed by some media as China's most wanted fugitive. He was returned from Canada in 2011 after a decade-long extradition battle and diplomatic negotiations between China and Canada. An agreement that he would not be executed was pivotal to his final return.

Liu Tao, a law professor with the People's Public Security University of China, told the Global Times that difficulties cooperating with Western countries were more about politics.

"If countries have more mutual interests in police affair or business, they are more likely to agree upon judicial treaties. Some economic cases, including Lai's case, were used for political purposes by some Western countries, such as damaging China's international status or image," Liu Tao said.

Experts said obstacles to cross-border arrests made those guilty of severe economic crimes, such as Lai, choose to flee to Western countries; however, others found that Southeast Asia was a cheaper alternative with fewer barriers to entry.

No money back guarantee

Transferring illicit wealth abroad can prove to be difficult. Zhang, for example, confessed that he tried to transfer money by investing around 500,000 yuan into a jellyfish business in Vietnam before the couple fled.

Liu Tao said that investments were a common method of transferring money out of China before an escape and these activities can cause huge economic losses.

"From a judicial perspective, most of these investments made with illicit money were legal abroad which make it very difficult to get the money back, even after the suspects were arrested," Liu said.

Both Wu and Liu said that they believe some countries refuse to sign extradition treaties with China because they found those investments beneficial, and negotiations regarding how much money China should be able to recover can take a long time.