A fellow prisoner posed as Walter E. Ellis in 2001 and gave a DNA sample for him, keeping the accused serial killer out of a statewide database and letting him avoid capture for years, according to a state Department of Justice memo.

It wasn't an isolated incident. DNA for about 12,000 felons convicted since 2000 is missing from the database, the department said Wednesday.

Even today, the failures in the system that allowed Ellis' bogus sample to slip through likely still exist, Wisconsin Attorney General J.B. Van Hollen said.

"Twelve thousand doesn't shock me. We know there were submissions not made," he said in an interview. "There are issues out there that still need to be corrected."

The missing samples would represent about 10% of all DNA profiles in the database, which law enforcement and prosecutors constantly rely on to solve crimes.

Officials learned about the widespread problem in the past week as they investigated why Ellis' DNA was not in the system. He is suspected of killing seven Milwaukee women over 21 years.

One of the victims, Ouithreaun Stokes, was killed in 2007 - six years after Ellis' DNA should have been on file with the state. A top state official has acknowledged she might still be alive if the sample had been there.

Milwaukee County District Attorney John Chisholm called the missing DNA samples "deeply disturbing."

"This is a huge deal, and it has to be corrected immediately," Chisholm said. "There are no excuses for this. There are none. It is unacceptable from a public safety standpoint."

If not for Ellis, the larger problem might not have been discovered, Milwaukee Police Chief Edward Flynn said.

"This investigation not only solved a crime but exposed a systemic problem, so it succeeded on multiple levels," Flynn said. "It is a serious issue. We need to be able to rely on the integrity of the DNA samples, that they are both accurate and complete."

Because Ellis is a convicted felon, his DNA should have been collected before he left prison in 2001. The Journal Sentinel reported last week that Department of Corrections computers indicated a sample was taken, but the Department of Justice, which runs the state database and the State Crime Laboratory, never received it.

The revelation of the 12,000 missing samples came after the Journal Sentinel filed an open records request last week asking for the names in the DNA database. The newspaper planned to compare that list with a list of felons convicted since 2000.

Authorities learned this week the phony sample was sent to the Crime Lab in February 2001. A scientist there realized the problem, but no one called the prison.

"That's mind-boggling," said state Rep. Mark Gundrum (R-New Berlin), a member of the Assembly Committee on Corrections and the Courts. "That is in the category of just so obvious it should be automatic. They need to start providing answers as to what happened here."

The 12,000 felons missing from the database were convicted between January 2000 and last week, said Gary Hamblin, the Department of Justice official in charge of the DNA investigation. The missing DNA spans the tenures of Van Hollen, Peg Lautenschlager and Gov. Jim Doyle, who was attorney general in 2001 when the fraudulent sample was submitted for Ellis.

"I certainly can't tell you why a Crime Lab analyst would not notify the DOC," Van Hollen said. "It was before my watch. There was no obligation for them to relay the information to the DOC, although it would be good practice. It is something we're going to continue to endeavor to do."

Doyle was on a trade mission and could not be reached Wednesday. His spokesman, Lee Sensenbrenner, referred questions to the Department of Corrections. Lautenschlager could not be reached.

Van Hollen didn't call for anyone to be held accountable.

Both Chisholm and Milwaukee County Sheriff David A. Clarke Jr. disagreed.

"This isn't a mistake, this is an abomination," Clarke said. "Let's go ask the victims of unsolved sexual assaults or other crimes if they feel anybody needs to be held accountable."

John Pray of the Wisconsin Innocence Project, which works to uncover wrongful convictions, said the news of the missing DNA has serious implications.

"Twelve thousand is a huge deal," Pray said. "It's amazing there are that many people who should be in the databank but aren't. It's really important that these (DNA profiles) be in there to convict the guilty, exonerate the innocent and prevent other crimes from happening."

Investigators have not uncovered corruption in the Ellis case, but the probe continues, Hamblin said.

"So far we have not uncovered any indication of that, but I can tell you, having been in law enforcement for over 40 years, if you were to come to me and say you found that, I would not be shocked," he said.

Michael Camp, who ran the lab in 2001, said he doesn't recall the Ellis case.

"That someone slipped through, it doesn't surprise me," he said, noting the overwhelming number of samples the lab was receiving at the time.

Not all the missing DNA samples resulted from inmate impersonation, Hamblin said.

He suspects that many of those without samples on file were convicted around the time the law took effect and were simply missed in the rush to collect DNA from everyone. Others likely never spent time in custody. DNA collection should have been a condition of being released from probation, he said, but for some reason that didn't happen.

About 70% of the felons whose DNA is missing from the database either are, or were at one time, under the supervision of the Department of Corrections, Hamblin said. The rest were probably never sentenced to prison and should have submitted their DNA to local law enforcement.

Authorities do not know how many felons without DNA samples are out on the street. The investigation will try to determine that, Hamblin said.

The Department of Corrections will review its DNA collection procedures, Secretary Rick Raemisch said in a statement.

"The Department of Corrections will work with the Department of Justice to make sure they have adequate procedures in place to notify us of a problem with a specimen they receive from us," the statement says.

Officials in Milwaukee said a system needs to be set up quickly to collect the missing DNA. Flynn said collection from prisoners and people on probation and parole should start immediately.

A database of felons who have not given samples also should be set up and made accessible to local police, Flynn said. That way, whenever police stop someone, officers can see if a sample is required and move to get it, he said.

Chisholm suggested going further, launching an effort to find the felons who have not given DNA, much like the hunt for unregistered sex offenders. Chisholm anticipated there will be more prosecutions as the missing DNA is collected.

"It has got to be corrected and done with a sense of urgency," Chisholm said. "We are talking about public-safety issues. They are not negotiable."

Ben Poston of the Journal Sentinel staff contributed to this story.