NEW YORK (CBSNewYork/AP) — An investigation into suspected cheating on New York state tests for licenses to drive such sensitive vehicles as school buses and hazardous-materials trucks has ensnared almost two dozen more people after 19 arrests in September.

The Manhattan district attorney’s office and the state inspector general’s office announced the additional indictments Wednesday. They involve 21 test-takers accused of paying as much as $4,000 to get the answers.

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All of the latest suspects have pleaded not guilty to false-filing charges.

“We entrust the holders of specialized licenses to drive our kids to school, transport dangerous materials, and perform other important tasks, all behind the wheels of large motor vehicles,” Manhattan District Attorney Cyrus Vance said in a news release. “It is critical that these drivers have the necessary skills and knowledge to perform these duties safely. The defendants are accused of fraudulently obtaining specialized licenses, putting at risk the lives of everyone who shares our roadways.”

Authorities say test-takers would leave the exam site with blank test forms. Someone else then filled in correct answers to questions on subjects such as brake safety and loading hazardous materials. The test-takers then returned to the site, handed in the forms and sometimes received interim licenses immediately.

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In September, 19 people were arrested in connection with the investigation, including eight alleged ring-leaders, eight alleged test takers and three security guards.

Eight defendants have already pleaded guilty.

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