It remains unclear why Richard H. Roberts, a New Jersey physician, contributed $1 million to help one member of Congress in south Florida, freshman Republican Allen West, win reelection.

Reached at his home last week, the main funder of a super PAC that has become the largest outside spender against West's Democratic opponent, construction executive Patrick Murphy, in one of the most closely-watched House races in the country, said he has retired from the pharmaceutical firm that he identified himself as heading in campaign finance forms. But he would say little else.

"I generally don't talk to press ...