NEW YORK (CNN/Money) - Former Tyco International Ltd. CEO Dennis Kozlowski pleaded innocent Wednesday to charges he tampered with evidence related to a tax-evasion case.

Kozlowski was indicted earlier this month on charges he conspired to avoid paying more than $1 million in sales tax on artwork he purchased.

Manhattan District Attorney Robert Morgenthau on Wednesday added to the charges, accusing Kozlowski, 55, of trying to hide a shipping invoice that allegedly helps prove he avoided paying the sales taxes on several paintings he bought, allegedly using funds borrowed from troubled manufacturing conglomerate Tyco.

In a June 4 indictment, Morgenthau alleged Kozlowski had avoided paying taxes on six paintings worth about $13.2 million. As part of that indictment, Morgenthau said Kozlowski had an art dealer ship five empty crates to Tyco's New Hampshire office in an effort to make it look like Tyco was buying five paintings, so he could avoid paying sales tax on paintings he already had bought for himself.

On June 4, Manhattan DA Robert Morgenthau displayed a copy of a painting Kozlowski allegedly bought without paying sales tax.

In Wednesday's indictment, the district attorney said Kozlowski removed the bill of lading for the shipment of those empty crates from a file of documents kept at Tyco's offices in Boca Raton, Fla., before having the file sent to the district attorney's office as part of its ongoing investigation.

Neither Kozlowski nor his new York lawyer,Stephen Kaufman, could be reached for comment. Kozlowski pleaded innocent to the initial indictment and was released on $3 million bail. His next court appearance in that case had been scheduled for Thursday.

The tampering charge is a felony, Morgenthau's office said. If convicted, Kozlowski faces up to four years in prison. He already faced 11 other felony charges and one misdemeanor charge from the prior indictment.

Shares of Tyco (TYC: down $1.58 to $11.97, Research, Estimates) fell more than 8 percent at midday Wednesday. Since December, the company has lost more than $86 billion in market capitalization.

Tyco would not comment on the latest news, aside from saying it was cooperating with the district attorney's investigation by supplying information. Neither Tyco nor the district attorney's office would comment on whether or not the company or other Tyco employees were subjects of the probe. The district attorney's office simply repeated Morgenthau's earlier assertion that the investigation would continue.

Kozlowski's indictment comes along with the public embarrassment of several other current and former chief executives, including former ImClone Systems (IMCL: up $0.13 to $9.08, Research, Estimates) CEO Sam Waksal, indicted on insider trading charges; Martha Stewart Living Omnimedia (MSO: down $3.20 to $10.40, Research, Estimates) CEO Martha Stewart, under investigation for trades she made in ImClone Systems stock; former Adelphia Communications CEO and founder John Rigas, accused of using off-the-books entities as a source of funds for his personal gain; and many more.

Kozlowski resigned as Tyco CEO the day before his first indictment, after trying unsuccessfully to restore investors' confidence, made shakier by questions about his compensation and his strategy for righting the company.

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Kozlowski has been credited with building Tyco into a $36 billion manufacturer during the 1990s, mainly through aggressive acquisitions. The Bermuda-based company makes fire alarms, security systems, bandages and other medical products, and undersea fiber-optic cable.

The company has struggled lately, hit by last year's recession and closer investor scrutiny of the company's accounting in the wake of the collapse of Enron Corp., the scandals associated with that and the seemingly endless parade of scandals that have developed since -- including Tuesday's announcement by WorldCom that it had uncovered improper accounting and would have to restate its 2001 and first-quarter 2002 earnings to the tune of nearly $4 billion.