Updated

The strain of anthrax that killed a Florida man last week may have been artificially modified, Florida newspapers Wednesday reported law enforcement sources as having said.

The anthrax samples taken from the body of Robert Stevens, 63; from the computer keyboard in his office at American Media, Inc., in Boca Raton; and from the nasal passages of Ernesto Blanco, 73, a mailroom worker in the building, all matched, officials said. Blanco is said to be in good condition at a local hospital.

Video: Anthrax That Killed Fla. Man Believed to Be Man-Made

The samples have "unique characteristics" linking it to a strain of the bacterium cultivated in an unidentified Iowa research facility in the 1960s, sources told the Miami Herald, adding that conclusive tests were not yet finished. The strain was being compared to samples kept in a library at the Centers for Disease Control in Atlanta.

Artificial origin would rule out accidental introduction to the American Media building, law enforcement sources told the Herald. However, the strain would still be treatable with penicillin and other antibiotics, sources told the Palm Beach Post.

No evidence of anthrax was found in Stevens' home, car or places he frequented, and his family has returned home, Palm Beach County officials said.

In contrast, the American Media building was still quarantined Wednesday, and 770 people who worked in or had visited the building were tested for exposure to anthrax. Results of the tests were not yet ready. Authorities were still waiting for another 70 employees to show up for testing.

FBI agents wearing white moon suits and gas masks scoured the facility, removing bags of evidence filled with plastic containers resembling Tupperware. No further sign of anthrax turned up.

"We have in essence gone into the building, cleaned the building out, taken all samples as possible, and are following any trail — any possible trail," President Bush said in Washington Tuesday. "Thus far it looks like it's a very isolated incident."

Attorney General John Ashcroft has stated there is no indication of terrorism in the anthrax case, but said the case could become a "clear criminal investigation."

American Media Inc. publishes the supermarket tabloids the National Enquirer, the Star, the Weekly World News and the Sun; Stevens was a photo editor for the latter. Its staff has moved to temporary quarters in nearby Delray Beach.

Interestingly, at least two of the Sept. 11 hijackers had subscriptions to American Media newspapers, investigators confirmed.

"We're not sure what to make of that yet," a source close to the inquiry told the Herald. "It may mean absolutely nothing."

Fox News has learned that authorities have tested places where the hijackers stayed and cars they used that were left behind at the Boston and Washington-area airports. Sources say so far no anthrax has been located on anything tied to the hijackers.

Authorities are not sure how the anthrax got into the American Media building, but one leading theory is that a jilted lover sent it in a letter to someone who worked there. FBI spokeswoman Judy Orihuela told the Post there was no evidence that a love letter to actress and singer Jennifer Lopez , mailed to American Media several weeks ago, was the source of the contamination.

Meanwhile, emergency officials responded to calls around the state about suspicious white powders being mailed or delivered to homes and businesses. The anthrax cases also prompted reports of possible infections in Texas and Wisconsin.

Firefighters in suburban Fort Lauderdale were quarantined for 12 hours, and officials closed a bank and law firm in Naples, on Florida's west coast. Dozens of people were sent to hospitals for tests, but there were no reports of anyone becoming sick.

Palm Beach County Health Department spokesman Tim O'Connor said on Tuesday that it was "highly unlikely" that anthrax could be transported through a white powder.

In Temple Hills, Md., outside Washington, an armed man sprayed a substance into a subway station during a scuffle with police Tuesday. Authorities took the man into custody and said it did not appear to be a terrorist act.

An Internal Revenue Service tax processing center in Covington, Ky., was locked down Tuesday after an employee reported receiving a letter that contained a white powder. Preliminary tests found no harmful substances, police said.

BioPort Corp., the only U.S. manufacturer of anthrax vaccine, has been unable to ship any of its product during its three years of operation. It has been stymied by its failure to meet federal drug agency standards for its renovated plant in Lansing, Mich.

Questions have arisen over BioPort's ability to produce the anthrax vaccine, and over whether the Pentagon's exclusive contract with the company has kept newer, better vaccines from being developed.

The Associated Press contributed to this report.