Clifford Baxter, 43, who had been Enron vice chairman before he left the company last year, was found in his black Mercedes Benz S500 sedan, parked in the median strip of a street near his $700,000 home in the Houston suburb of Sugar Land.
A suicide note was found at the scene, but its contents were not immediately disclosed by Sugar Land police.
Baxter was pronounced dead at the scene, and a justice of the peace later ruled the death was a suicide, but an autopsy was ordered.
"An autopsy will be conducted, and we will continue to investigate," Sgt. Truman Body said.
A revolver was found in the locked car, he said, and there were no signs of foul play apparent at the scene, Body said.
Baxter had resigned from Enron in May 2001 after a decade with the Houston company working his way through several top-level executive posts, Enron spokesman Eric Thode said.
"We are deeply saddened by the tragic loss of our friend and our colleague, Cliff Baxter. Our thoughts and prayers go out to his family and friends," an Enron statement said.
Baxter resigned several months before the Houston company filed for Chapter 11 bankruptcy in December. He had complained about some of the company's practices, according to a recently disclosed letter from Sherron Watkins, a vice president for corporate development.
"Cliff Baxter complained mightily to (then-President Jeff) Skilling and all who would listen about the inappropriateness of our transactions with LJM (one of the partnerships that Enron created)," she wrote in August to former Chairman Ken Lay.
At the time of the resignation, Skilling said Baxter had made "a tremendous contribution to Enron's evolution, particularly as a member of the team that built Enron's wholesale business."
When he departed, Baxter said he wanted to spend more time with his family, according to the Houston Chronicle.
Baxter was one of 29 former and current Enron executives and board members named as defendants in a civil lawsuit filed in U.S. District Court. Shareholders charged the executives made $1.1 billion by selling Enron stock between October 1998 and November 2001, the Chronicle said.
The House Energy and Commerce Committee was trying to question Baxter along with other Enron officials but had not issued a subpoena for his testimony, sources told CNN. Lawyers were negotiating to get his cooperation.
Baxter was born Sept. 27, 1958, in Amityville, N.Y. He received a bachelor's of science from New York University in 1980 and an MBA from Columbia University in 1987. He served as a captain in the Air Force from 1980-85.
The Houston energy company filed for bankruptcy on Dec. 2, the largest such filing in U.S. history, putting thousands of its own employees out of work and wiping out the retirement savings of both employees and many outside investors.
Much of Enron's collapse was amid questions about the company's accounting practices. The company is the focus of overlapping investigations by the Securities and Exchange Commission, several congressional committees and the Justice Department.