Chicago police and the FBI are investigating a businessman whose name was signed to an extortion letter demanding $1 million from the manufacturer of Tylenol and threatening to distribute more cyanide-poisoned Tylenol capsules, Chicago Police Superintendent Richard Brzeczek said yesterday.

But later in the day, Illinois Attorney General Tyrone Fahner, chief investigator in the case, said the latest lead apparently "will not be relevant" to the probe into the cause of Tylenol-related deaths.

Other investigators said the extortion letter may have been written by a "kook" simply trying to take advantage of the Chicago tragedy.

Brzeczek said the letter was signed with the name of a "local businessman" and apparently was mailed after the seven persons died in Chicago last week after taking Tylenol capsules tainted with cyanide.

The businessman has voluntarily submitted to questioning by FBI agents and provided handwriting samples, an attorney for the businessman told reporters.

Bank officials yesterday said they had been ordered to turn over the financial records of a former customer in connection with the Tylenol case. The FBI refused to comment on the development.

According to reports in The Chicago Sun-Times, a letter with the word "Tylenol" written on the envelope was sent to McNeil Consumer Products Co., the makers of Tylenol, demanding that $1 million be sent to a box at the Continental Illinois National Bank and Trust Co. in Chicago, or more people would die.

The Sun-Times quoted unidentified sources as saying that the box was rented by a Chicago businessman, and the extortion letter was traced to a defunct business the same man once operated.

So far, police said, there is no proof the businessman wrote the extortion letter. The man in question, according to newspaper reports, is a once successful stockbroker who had suffered recent considerable financial reverses.

Meanwhile, members of an investigative task force headed by Fahner have reported no substantial clues in the case.

"We're back to the generally described suspects," Fahner said yesterday. Those suspects include disgrunted employes, people seen loitering in stores or acting suspiciously and people who have threatened to get even with someone.

Brzeczek said he was confident the killings would be solved, but admitted that as the investigation wore through its eighth day, officials were left with few promising leads.

"As times passes from the initial event, it becomes more difficult," Brzeczek said.

"We're still in the process of trying to understand the scenario of events as to how the cyanide got into those bottles," the superintendent said. "That's what you need to do to tie it in with a specific person."

In another development, a Chicago police detective was sent to Sheridan, Wyo., to aid in determining if the July 26 death of Jay Adam Mitchel, 19, was tied to the contaminated Extra-Strength capsules.

Sheridan County Coroner Jim Kane told United Press International that he received a verbal report from the the University of Utah Center for Human Toxicology that Mitchel's body contained lethal levels of cyanide. But Kane would not say that Mitchel's death was possibly Tylenol-related.

Tylenol, meanwhile, has ordered several machines from the Corona Treating and Cap Sealing division of the Pillar Corp. to put foil seals on their bottles, allowing consumers to know when they have been tampered with.