Glendale, CA -- A former respiratory therapist who had once confessed to killing 50 patients by euthanasia at a Los Angeles-area hospital where he had worked during the 1990s, was arrested Tuesday on six murder charges following a three-year investigation in which 20 bodies were exhumed and checked for signs of foul play.

Efren Saldivar, 31, was pulled over and arrested by Glendale police shortly before 6 a.m. PST as he drove to work and was jailed on six first-degree murder charges. He was scheduled for arraignment in state court.

Saldivar is no stranger to the police. He had been given the nickname "Angel of Death" by the Los Angeles media after he confessed to detectives that he had administered fatal drug overdoses to some 50 patients at Glendale Adventist Medical Center, where he worked from 1989 through 1997.

Saldivar, however, recanted his confession a short time later and was released with no charges filed due to a lack of evidence; he said at the time that he had been suffering from depression and other mental problems and had fabricated his confession.

Police did not drop the case, however, and during the following 34 months, a task force of detectives examined 170 deaths, plowed through volumes of medical records and exhumed the bodies of 20 patients who had died at Glendale Adventist to check for traces of powerful muscle-relaxing drugs.

Tests on post-mortem tissue samples were conducted at the Lawrence Livermore National Laboratory outside San Francisco.

Toxicological tests revealed the presence of the drug Pavulon in the remains of the six victims and it was not part of legitimate treatment of five of those patients, County District Attorney Steve Cooley said at a news conference Wednesday.

Hospitals frequently use Pavulon to stop the normal breathing of patients who are put on artificial respiratory devices, said Deputy District Attorney Al Mackenzie, who will handle the case.

``If you're going to do surgery, you're going to put the person on an artificial breathing device,'' Mackenzie said. ``If you give the person the drug Pavulon and don't create an artificial means to breathe, they die.''

"We have evidence to conclude that six of these patients were indeed murdered," Glendale Police Chief Russell Silverling said at a Tuesday afternoon news conference.

Saldivar had been originally taken into custody in March 1998 after hospital officials received a telephone tip that he had been involved in a number of deaths at the 450-bed facility. He was released after two days in custody when no independent evidence was found to prove his confession.

In his short-lived confession, Saldivar indicated the deaths were mercy killings and said he had been angry that heroic measures were being taken to keep terminally ill patients alive.

Saldivar allegedly told police he committed dozens of mercy killings at the medical center between 1989 and 1997. He told police he considered himself the ``Angel of Death.''

Saldivar lost his respiratory therapist license and was not working in a hospital at the time of his arrest. He lived in nearby Tujnga and worked as an apprentice electrician.

Relatives of Jose Alfaro Sr., 82, who died Jan. 4, 1997, after being hospitalized with severe pneumonia, emphysema and chronic pulmonary and arterial disease, said police told them that Pavulon was found in Alfaro's system.

``Who is he (Saldivar) to kill_'' asked his wife Cecilia Alfaro. ``That was my husband. We were married in 1941. I was only 26. And this guy killed and he had no right to kill.''

Alfaro's cause of death was originally listed as cardiorespiratory failure. The Alfaros, of Glendale, have hired a lawyer to file a wrongful death lawsuit.

Police Chief Russell Siverling said Tuesday that investigators had an ``initial inkling'' that Saldivar may have killed patients at other hospitals where he moonlighted.

Saldivar is indigent and will need a public defender in the criminal case, said attorney Terry M. Goldberg, who represents the man in a half-dozen wrongful-death lawsuits.

``It appeared to me that he was very disturbed, very distraught and very upset,'' Goldberg said at his own news conference Wednesday. ``I hope people will be patient in ferreting out the truth in this case.''

Glendale hospital spokeswoman Alicia Gonzalez said officials had no comment. But the hospital issued a letter to patients and visitors saying the hospital had cooperated with police and that doctors met with more than 250 families to review medical records.