An Indonesian court has acquitted two policemen charged over the Kanjuruhan stadium crush last year, angering relatives of victims in the tragedy. Police had been blamed for triggering the crush that night after firing tear gas at spectators on the field. That led to a stampede that killed 135 people - the second deadliest football disaster in history. Devastated families in the courtroom on Thursday erupted in anger and disbelief following the verdict. A woman whose teenage son was killed in the crush said: "Many people have died, how come they are now free?" Susiani had clutched a photograph of her 16-year-old son throughout the court hearing. She looked shattered when the verdict was read out. The court sentenced one officer to 18 months prison for criminal negligence, but found two other senior policemen not guilty of the same charges. One commander, Bambang Sidik Achmadi, had been accused of ordering his police unit to fire tear gas at match attendees. But the local court in East Java found that such charges "had not been proven". Police commissioner Wahyu Setyo Pranoto was also acquitted. "There is no causal relationship between the defendant's actions and the victim. The negligence element is also not proven. So the defendant should be declared not guilty," said chief judge Abu Achmad Sidqi Amsya. Human rights groups have criticized the verdict, questioning the legal procedure. Families of the victims had been critical of the trial since it started in January behind closed doors. Irfan, head of local rights group Kontras, said it was "reasonable to suspect that the panel of judges is acting unfairly in the trial process of this case". He urged prosecutors to appeal the decision. Hasdarmawan, the police officer who was found guilty, was sentenced to 18 months - half the sentence sought by prosecutors. The chief judge said he had failed to "predict a situation that was actually quite easy to anticipate". "There was an option not to fire [the tear gas] to respond to the supporters' violence," judge Amsya said. Last October, supporters of the home team Arema FC invaded the stadium's pitch after their side suffered a 3-2 defeat to their fierce East Java rivals Persebaya Surabaya. Police responded by firing tear gas at those on the pitch and fans in the stadium, who tried to flee. That prompted a crowd crush at the narrow exits of the stadium. At least 40 children were among those killed that night. More than 600 people were injured. Last week, the court had jailed two football club officials over the tragedy. Abdul Haris, the chairman of the home club's organising committee, was sentenced to 18 months in prison. The club's security officer Suko Sutrisno, was jailed for a year. Club officials had failed to put in place adequate safety measures, the judge said. The Kanjuruhan disaster has been a major source of national grief in Indonesia. It is the second-deadliest football disaster in history, after the 1964 stampede in Lima, Peru where 328 people died. A report last year by Indonesia's human rights body, Komnas HAM, ruled that the tragic incident had been sparked by police's tear gas. A police chief and nine elite officers were removed from their posts after the incident. ——BBC