The New York Times reports: A decade after wisps of anthrax sent through the mail killed 5 people, sickened 17 others and terrorized the nation, biologists and chemists still disagree on whether federal investigators got the right man and whether the F.B.I.’s long inquiry brushed aside important clues.

Now, three scientists argue that distinctive chemicals found in the dried anthrax spores — including the unexpected presence of tin — point to a high degree of manufacturing skill, contrary to federal reassurances that the attack germs were unsophisticated. The scientists make their case in a coming issue of the Journal of Bioterrorism & Biodefense.

F.B.I. documents reviewed by The New York Times show that bureau scientists focused on tin early in their eight-year investigation, calling it an “element of interest” and a potentially critical clue to the criminal case. They later dropped their lengthy inquiry, never mentioned tin publicly and never offered any detailed account of how they thought the powder had been made.

The new paper raises the prospect — for the first time in a serious scientific forum — that the Army biodefense expert identified by the F.B.I. as the perpetrator, Bruce E. Ivins, had help in obtaining his germ weapons or conceivably was innocent of the crime.

Both the chairwoman of a National Academy of Science panel that spent a year and a half reviewing the F.B.I.’s scientific work and the director of a new review by the Government Accountability Office said the paper raised important questions that should be addressed.

Alice P. Gast, president of Lehigh University and the head of the academy panel, said that the paper “points out connections that deserve further consideration.”

Dr. Gast, a chemical engineer, said the “chemical signatures” in the mailed anthrax and their potential value to the criminal investigation had not been fully explored. “It just wasn’t pursued as vigorously as the microbiology,” she said, alluding to the analysis of micro-organisms. She also noted that the academy panel suggested a full review of classified government research on anthrax, which her panel never saw.

In interviews, the three authors said their analysis suggested that the F.B.I. might have pursued the wrong suspect and that the case should be reopened. Their position may embolden calls for a national commission to investigate the first major bioterrorist attack in American history.