MILWAUKEE, WI (WTAQ) - Milwaukee County officials say there are no more murder cases from the past 20 years in which those convicted would go free with the proof of modern DNA testing.

District attorney John Chisholm had staffers and experts review 21-hundred cases – and there were no indications that anyone else had been wrongly convicted.

The review started last June, after it was found that serial killer Walter Ellis was linked by DNA evidence to three murders in which someone else had already been suspected. Two have gone free, and the other was charged but acquitted.

Attorneys for the Wisconsin Innocence Project at UW Madison said they were shocked and disappointed by the finding.

The project uses students to dig up DNA evidence that would up overturning some major convictions in recent years.

An attorney for William Avery, one of the three suspects exonerated, said it’s “impossible to understand” that a single case could be found where a person might have been wrongly convicted.

Chisholm said the study included three detailed levels of review – and a DNA expert was involved in the study’s final stage.

Ellis has pleaded no contest to killing seven women over a 21-year period in Milwaukee. And DNA had linked three other murders to him.