Adelphia Communications Corp. inflated the number of its cable-TV subscribers by between 400,000 and 500,000, or as much as 10 percent of the company’s total customer base, according to people familiar the situation. In addition, investigators have uncovered evidence that Adelphia kept two sets of accounting books for its capital expenditures, one of which was shown to Wall Street and boosted the amount Adelphia spent to upgrade its cable systems.

The SEC is also focusing heavily on the role Deloitte & Touche played as Adelphia’s auditor. Regulators are taking a close look at what Deloitte knew about related-party transactions, co-borrowing arrangements and subscriber inflation, said a person close to the situation. The SEC is concerned that Deloitte “knew things and didn’t bring them to the board’s attention,” this person said.