DaVita Inc. announced Tuesday that Denise Fletcher stepped down as senior vice president and chief financial officer at the same time the El Segundo-based dialysis firm is in the middle of a $3.4 billion acquisition of Gambro Healthcare while under investigation for the third time in four years.

DaVita said that the decision, effective April 15, was reached by "mutual agreement," but offered no other details. Tom Kelly, the firm's executive vice president, will assume the role of acting chief financial officer while continuing with some of his current responsibilities. The search for a new CFO will begin immediately, DaVita said in a press release.

The nation's No. 2 dialysis center operator has been under investigation since early March by the U.S. Attorney's Office in the Eastern District of Missouri for information dating back to 1996 related to its use of pharmaceuticals and its physician relationships the third subpoena it has been hit with in four years.

And in mid-February, the Federal Trade Commission signaled concern over the potential anti-competitive effects of a proposed merger between DaVita Inc. and Gambro Healthcare, requesting more information about the deal.

Shares of DaVita sank nearly a dollar Tuesday on the news in afternoon trading, but then recovered. The stock settled at $41.80, up 0.1 percent.

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