An aide for Missouri Congressman Sam Graves says the Republican is not sure why he received a $1,000 donation from a former Westar Energy executive.

The Topeka-based energy company and its executives contributed a total of $56,500 to the campaigns of several House Republicans.

Congressman John Conyers, a Michigan Democrat, has requested an investigation into the donations.

Internal Westar documents claim the donations were intended to help secure legislation that could have saved the company billions of dollars. The provision never passed.

Graves received a thousand-dollar check from former Westar chief executive David Wittig last June.

Wittig resigned from Westar in November to defend himself against bank fraud charges unrelated to Westar. He has pleaded not guilty.