Assailants hacked at bystanders with knives and machetes, killing 29 people and injuring 141 in attack in Yunnan province

A court in southern China sentenced three people to death and one to life in prison on Friday for perpetrating a gruesome knife attack on a railway station this spring, an incident that shocked the country and underscored the severity of ethnic conflict in the north-western region of Xinjiang.

At the end of a one-day trial, prosecutors in Kunming, the capital of south-west China's Yunnan province, found four defendants guilty of orchestrating the attack on 1 March, in which eight black-clad assailants indiscriminately hacked at bystanders with knives and machetes, killing 29 people and injuring 141.

Police shot four attackers dead at the scene, and captured one. State media has offered conflicting accounts of when the remaining four attackers – three men and one woman – were detained.

Prosecutors charged all four suspects with intentional homicide. Iskandar Ehet, Turgun Tohtunyaz and Hasayn Muhammad were convicted of organising and leading a terror group, and sentenced to death. The fourth, Patigul Tohti, was convicted of joining a terror group and received a life sentence.

While Xinhua, the state news agency, did not explicitly state their ethnicities, it strongly implied that the four defendants were Uighurs, a predominantly Muslim, Turkic-speaking group from Xinjiang.

The region has seen an explosion of violence over the past year – 323 people have died in trouble related to the region's ethnic struggles since last April, according to the Associated Press, with police officers accounting for half of those deaths. Authorities have blamed the clashes on the spread of separatism and religious extremism, while Uighur groups abroad call them a desperate expression of economic, cultural and religious grievances.

China has cracked down on the region in the wake of the attacks, waging a so-called "strike-hard" campaign against terrorism. Authorities broke up 200 "terror cells" in Xinjiang last year, up from 140 in 2010, state media reported.

The supreme people's procuratorate, the country's top prosecuting body, has encouraged prosecutors to fast-track cases involving suspected "terrorists, religious extremists and manufacturers of firearms and explosives", especially in Xinjiang.

"Counter-terrorism is to be a priority of prosecutors as part of tough measures against the 'three evil forces' – terrorism, separatism and extremism. Human trafficking cases will also be fast-tracked," Xinhua said on Friday morning.

Chinese prosecutors are often under intense pressure to swiftly crack cases of political importance, raising the risk of forced confessions and, in some cases, wrongful convictions, according to Maya Wang, a Hong Kong-based researcher for Human Rights Watch. Expediting terrorism cases, she said, could potentially exacerbate the problem.

"The procuratorate has two functions: monitoring police abuse, and on the other hand, helping the police solve crimes – so there's a conflict of interest, which is a major problem in China's criminal justice system," she said. "The fact that terror suspects are not given the protections given to other criminal suspects under Chinese law also means the government risks not punishing the real perpetrators behind the attack, and so risks further incidents."