TAIPEI - Three Taiwanese men suspected of murdering a couple more than 20 years ago were acquitted for the last time by a Taiwanese court on Friday, ending a controversial marathon legal process that has gripped the whole of Taiwan.

Su Chienhuo, Liu Pinglang, and Chuang Linhsun, who were accused of murdering Wu Minghan and his wife in 1991 at their home in the northern Taipei county, later renamed New Taipei city, were cleared of all charges and declared innocent.

Under Taiwan's legal system, the verdict is final and can not be appealed.

The ruling puts an end to one of the most controversial murder cases in Taiwan's history, one that has raised serious questions about the conduct of the police officers and prosecutors who handled the case and sparked wide debate over the merits and deficiencies of the legal system.

The prime suspect, Wang Wenhsiao, was found guilty and executed in 1992. Police interrogations of Wang had also implicated Su, Liu and Chuang in the crime.

Taiwan's courts have since given varying verdicts in the case as new pieces of evidence have continue to surface and the island's legal system has gradually evolved.

In 1992, a district court of Taiwan declared the three suspects guilty and gave each of them a death sentence. Since then, various courts have given rulings that have ranged wildly from the death penalty to proclaiming the suspects innocent.

Each time, the court's ruling raised great controversy as the media and public fiercely debated not only the ruling itself but also the broader issue of the island's legal system.

Some argued that alleged illegal acts by police officers and prosecutors undermined the foundation of the case, but others worried whether the system could work efficiently when it came to nailing the real suspects in a highly complicated murder case.

The trials further gripped the attention of the public after media reported that the victims' son, only six years old at the time of the murder, was later diagnosed with muscular dystrophy and became completely paralyzed.

The tragic development aroused immense sympathy and some members of the public linked the son's illness to the great agony of a child forced to witness the brutal murder of his parents, a claim that was later medically refuted.

Taiwan's authorities even turned to the expertise of legendary Chinese-American crime scene investigator Henry Chang-Yu Lee for help.

In 2009, Lee, after reconstructing the crime scene, concluded in a report that Wang was probably the sole culprit in the murder, giving further weight to the suspects' claim of innocence.

Given the extraordinary nature of the case, the three suspects have largely remained free during the long and dramatic legal process.