An Illinois judge acquitted a man of murder Wednesday, more than two decades after jurors convicted him by relying on ballistics that proved to be wrong.

Supporters of 53-year-old Patrick Pursley clapped in a Winnebago County courtroom when Judge Joseph McGraw issued his ruling, saying prosecutors had scant evidence to prove Pursley’s guilt.

The ruling caps the long journey Pursley undertook to prove his innocence. He represented himself for years and lobbied Illinois lawmakers to pass a law allowing ballistics to be retested using technology not available when he was convicted. The Integrated Ballistic Identification System, or IBIS, uses much higher-resolution and multi-dimensional images for ballistics analysis and ultimately matches shell casings to guns.

In Pursley’s case, it showed that the gun used to convict him was not the gun used in the 1993 fatal shooting of 22-year-old Andy Ascher in Rockford, Illinois.

So far, IBIS has been primarily used by law enforcement to catch and convict criminals, not to prove their innocence. That’s because Illinois remains the only state in the country that allows defendants in post-conviction appeals to use the system to retest ballistics.

Pursley got a new trial in 2017 and chose to have McGraw decide it instead of a jury.

Pursley seemed speechless after the ruling.

“Forgive me, I’m still numb,” he told a television reporter.

Prosecutors had maintained that Pursley killed Ascher during a robbery while he sat in a car with his girlfriend. But they had no physical evidence connecting Pursley to the crime and no eyewitnesses. The centerpiece of their case was the conclusion from their ballistics expert who testified during the 1994 trial that the bullets that killed Ascher could only have come from the gun authorities recovered and connected to Pursley.