An independent review of the Houston police crime lab has found serious problems with DNA and blood-evidence analysis in dozens of criminal cases from 1987 to 2002, including three death penalty cases.

All three death-row inmates are still alive, and prosecutors were already reviewing their cases.

The report by former Justice Department inspector Michael Bromwich was the latest hit for the troubled lab, which had its DNA section shut down in 2002 when an audit revealed problems with DNA analysis.

"Our work to date in reviewing cases analyzed by these sections reflects a level of performance completely unacceptable in a forensic science laboratory providing critical support to the criminal justice system," the report said.

Bromwich is reviewing about 2,700 cases originally analyzed by the lab's six forensic departments. So far, 1,100 cases have been reviewed. Nearly 40 percent of DNA cases and 23 percent of blood evidence cases had major problems, the report found.

The investigation found "major issues" in 27 of the 67 DNA cases that had been analyzed, as well as 18 blood evidence cases, Bromwich said.

The three death penalty cases involve inmates Alex Guevara, Franklin Dewayne Alix and Juan Carlos Alvarez. They are being reviewed as part of an examination of all death row cases with questionable DNA evidence, prompted by the 2002 lab audit, said Harris County District Attorney Chuck Rosenthal.

In the case of Alix -- convicted of capital murder -- none of his DNA was on the evidence the lab tested, yet the lab told prosecutors the results were inconclusive, according to Bromwich's report. In Alvarez's case, the lab drew conclusions based on weak DNA results, while the lab said it found Guevara's DNA on evidence when it should have ordered retests, the report said.

Houston police officials said they would continue to try improving DNA and blood-evidence analysis.

"My main concern is to make sure nobody is currently in jail that shouldn't be," Executive Assistant Chief Martha Montalvo said.

Since early 2003, the Houston police and the Harris County district attorney's office have worked with outside DNA laboratories to review more than 400 criminal cases involving DNA testing by the Houston lab.

So far, one man, Josiah Sutton, was released from prison after serving about five years of a 25-year sentence for sexual assault. He was pardoned in 2004.

A judge released and recommended a new trial for a second man, George Rodriguez, who was imprisoned for 17 years for kidnapping and rape. Problems in his case surfaced separately from the lab investigation.