FORT WORTH - A review of three years' worth of DNA evidence processed by the Fort Worth Police Department's crime lab is under way after a proficiency test revealed that a senior forensic scientist did not follow proper procedures and protocol.

The review will involve almost 100 cases handled by the crime lab. Prosecutors in the Tarrant County District Attorney's office said they were angry because city officials didn't address problems called to their attention three years ago.

Prosecutors, who have come to rely on DNA evidence to help make cases, said they will conduct a criminal investigation into the workings of the DNA crime lab.

Karla Carmichael, the forensic scientist whose proficiency test raised questions, was placed on paid leave Friday. She joined the crime lab in 1999.

Deputy Police Chief Larry Curtis said DNA experts with the University of North Texas Health Science Center recently raised concerns about Carmichael's proficiency test that mirrored those of the DNA scientist who initially reviewed her test results. In a proficiency test, the DNA analyst is given a sample to evaluate; the analyst's procedures and results are then reviewed by another scientist in the lab.

The questions about the reliability of DNA results are the latest setback for the crime lab, which is just beginning to address case backlogs, staff shortages and an inadequate facility.

The lab stopped doing DNA testing in October after questions about Carmichael's work prompted prosecutors to not pursue the death penalty in a capital murder case. Prosecutors said second-opinion DNA test results by the Tarrant County Medical Examiner's office conflicted with those done by Carmichael.

The integrity of Carmichael's work was at issue again last week during a murder trial.

Curtis said lab director Phil Aviles, who was hired nine months ago, is reviewing all DNA cases tested by scientists, including Carmichael, in the lab in the past three years.

In its initial stages, Curtis said, the review has found nothing to indicate Carmichael "deliberately did something to alter a case."

Carmichael referred questions to her attorney, John Hunter Smith with the Combined Law Enforcement Association of Texas. Smith said Carmichael is scheduled to meet with police administrators Thursday to discuss her employment status.

"We look forward to presenting our side of the story regarding the past practices of the crime lab which Ms. Carmichael is now being subsequently punished for," Smith said. "Ms. Carmichael stands by the work she has done during her tenure with the Police Department."

Alan Levy, chief of the criminal division for the district attorney's office, received a copy of UNT's findings Friday. He said he was not shocked by what he read, noting that he and other prosecutors have brought concerns about a "long series of problems of the crime lab" to the city's attention numerous times over the past three years.

"Periodically we have re-emphasized our position that the crime lab needed to be re-examined," Levy said. "We didn't get any response from anybody in the city, either from the police administration or the City Manager's Office."

The contents of the UNT letter, dated March 26, were not disclosed.

Police Chief Ralph Mendoza was out of town Friday and Saturday.

Assistant City Manager Libby Watson said the Police Department has been actively addressing concerns raised about the DNA lab, including bringing in the DNA experts from UNT after questions about Carmichael's test results were raised in October.

Watson said the large-scale review was initiated after the UNT experts examined Carmichael's proficiency test.

"The chief directed that the district attorney's office be notified that, at this point, we don't have any confidence in any of her cases until we can conduct a review of all of them," Watson said.

"It's one of those cases where what you don't know can hurt you, which is why we've jumped into investigating this so fully," she said.

Pat Kneblick, the executive deputy chief, said the Police Department has been making changes to improve the lab.

"We've known and been trying to work at improvements in the crime lab and recognize that was a weakness," Kneblick said.

Fort Worth isn't the only large Texas city with crime lab problems.

An independent quality-assurance audit of Houston's DNA testing section, conducted by the Department of Public Safety and the Tarrant County Medical Examiner's crime lab, identified several deficiencies in documentation and record keeping as well as in the handling of evidence samples.

Results from the audit prompted Houston police in January to suspend DNA testing in the lab until the deficiencies can be corrected and the cases reviewed.

Last month, Josiah Sutton was freed from prison after retesting of evidence used to convict him of rape in 1999 found that the Houston lab's analysis was flawed.

"Of course, we don't want to get into a situation like Houston has gotten into," Curtis said. "We're always concerned about whether or not analysts have provided a result or testimony that may have unjustly incarcerated someone."

Curtis said that in addition to Aviles' internal review, the Police Department's major case unit will soon begin an inquiry to determine whether a criminal investigation is warranted.

"Their role will be to coordinate with Phil and whoever else that we may bring in to look at the cases to determine whether or not something was done deliberately to alter a result or to change a document," Curtis said.

Levy said the police investigation will be separate from the one done by the district attorney's office.

"The only question is who's going to conduct it, who's going to be involved and how many prosecutors," Levy said. "It's not an inquiry. It's a criminal investigation."

Levy said the problems in the DNA lab have prompted his office to seek independent testing on cases where DNA was vital to the case during the past two years.

DNA, or deoxyribonucleic acid, is genetic material. Each person has a unique DNA pattern that can be determined by testing tissue such as hair or body fluids. DNA tests use those unique patterns to determine whether a person is linked to hair or body fluids found at a crime scene.

Levy said he has also notified defense lawyers, advising them to seek their own testing as well.

"We're not in the situation that Houston is in," Levy said. "I don't think it's going to result in a lot of post-conviction litigation, because we protected the office and the state from using that kind of evidence."

On Friday, Levy forwarded a copy of the 2 1/2-page UNT letter about Carmichael to Larry Moore, president-elect of the Tarrant County Criminal Defense Lawyers Association. On Monday, Levy plans to send the letter to individual defense lawyers.

Curtis and Aviles declined to release the letter to the Star-Telegram.

Moore said the letter was disconcerting, but he praised the district attorney's office for bringing it to the group's attention.

"Anytime you're talking about some improprieties or problems in DNA testing, it's very important because it's such powerful evidence," Moore said. "If the processes that have been used are incorrect, and the results are thus suspect, it really calls into question a lot of evidence that may have already been admitted into criminal cases or cases that are pending."

Moore said defense lawyers had heard about crime lab problems but may not have been as vigilant in seeking independent DNA testing. Moore said he has handled cases in which Carmichael performed the DNA tests.

"This information makes me look back and say I should have done this differently," Moore said. "I'm afraid there's going to be a lot of other people in the same position."

When questions about Carmichael's work surfaced in the October capital murder case, she stood by her results. Curtis said Carmichael was never disciplined in the case.

"At this point, we thought this was a training issue," he said. "That's how we anticipated handling it, by providing additional training, trying to make sure we had all the right standards and procedures in place."

But prosecutors said they would no longer accept the lab's DNA testing unless the results were verified by the Tarrant County Medical Examiner's Office or UNT, which is reviewing lab work and the lab's procedures and protocols.

As a result, Aviles said, the lab is sending DNA for testing to other labs until scientists can become certified to conduct DNA analysis.

"The only thing we are doing at the present time is identifying cases, pre-screening cases for blood, body fluid, what have you; and then any DNA, we are sending that out," Aviles said.

Aviles said scientists are still entering DNA profiles completed by outside contractors into the Combined DNA Index System, or CODIS.

CODIS enables crime labs to search for possible DNA matches between evidence at the scene and convicted offenders on the local, state and federal levels. It can also help agencies link a case with no identified suspect to other no-suspect cases.

Last month, cases examined by the Houston police crime lab were purged from CODIS and the FBI's National DNA Indexing System, at the request of Houston Police Chief C.O. Bradford.

Fort Worth Mayor Kenneth Barr said the questions about a scientist's work and the subsequent review and investigation have not been brought to the City Council's attention.

"It is a serious matter, and we'll see that it gets serious attention in determining what are the appropriate steps at this point in time," Barr said. "It concerns me very much to hear that there's a likelihood that there's a problem."

In February, the council approved using $1.6 million from the Crime Control and Prevention District to build a new lab. The council also approved spending $120,000 from the district's reserve funds so that the police lab can gain immediate DNA certification.

But the integrity of the scientists' work was not discussed.

Councilman Chuck Silcox said Saturday he was troubled that the lab's credibility is being questioned. Silcox said the review of cases should be done by an outside DNA expert.

"How can [the public] trust us with what we've brought forward when one or more scientists have not done a correct job?" he said. "Have we put people in prison because of that? Have we released people who didn't need to be released?"

Last week, defense lawyers for Curtis Wayne Pope Jr., a 40-year-old man convicted Friday of murder, frequently attacked the crime lab's credibility outside the presence of the jury.

Called to testify, Carmichael was repeatedly asked about problems in the crime lab and why the district attorney's office is retesting cases analyzed by lab scientists.

Carmichael, who was among lab workers who repackaged samples from the case to send to an independent lab for testing, told lawyers that concerns surrounding the lab have focused on "the actual data generated through DNA analysis, which we did nothing like that on this case."

"You are the party responsible, though, for obtaining the specimen of -- the known samples of Curtis Pope in this case, correct?" asked defense attorney Stephen Handy, according to testimony transcripts.

"Yes," replied Carmichael.

"That's a pretty important role, isn't it?" he asked.

"Yes," she said.

"And that's done by a lab that's under, I think it's fair to say, scrutiny at this point?" Hardy asked.

"Correct," Carmichael said.

Staff Writer Melody McDonald contributed to this report.