The statistics were provided in the Annual Business report of the IRS' Criminal Investigation unit, which was issued this week. In the case of questionable refunds, the number of investigations has fallen by 95.2 percent since 2013. Over the same period, 14.2 percent fewer cases brought against abusive preparers and the number involving the hot area of identity theft were down 48 percent.

The agency's chief, Richard Weber, pointed to the impact of the budget cuts. "Having hired only 45 agents in the last three years, attrition was catching up to us and our staffing levels hit their lowest level since the 1970's," he says. "We finally came to realize that fewer agents and staff really do mean fewer cases."

The agency closed fiscal 2015 with 2,316 special agents, down 31.1 percent from
an all-time high of 3,363 in 1995. The impact, the IRS says, shows up in the recent statistics. There were 3853 investigations initiated in 2015 down 27.9 percent from 5,314 in 2013.

There were 776 identity theft cases started in 2015, a decline of 48 percent from 1,492 in 2013. Seven hundred ninety were sentenced in the most recent year, off 80.4 percent from 438 two years ago.

In terms of abusive preparers, there were 266 investigations initiated in 2015, a decline of 13.9 percent from 309 two years ago. Two hundred four were sentenced last year, a 9.7-percent rise from 186 for the same period two years earlier.

The IRS began 775 investigations into questions refunds in 2015, down 47.8 percent from 1,513 in 2013. However the number of sentence rose to 73 percent to 839 from 485.