WASHINGTON (Reuters) - The Senate Ethics Committee on Thursday dismissed a complaint against Sen. David Vitter, a suspected patron of a prostitution ring headed by a woman who killed herself last month.

In a letter to the Louisiana Republican, the panel said the conduct at issue allegedly occurred before his Senate candidacy and time in office. In addition, it did not result in his being charged criminally, the committee said.

As a result, the panel said it did not have jurisdiction, dismissing "without prejudice" the complaint filed by Citizens for Responsibility and Ethics in Washington, or CREW, a private watchdog group.

The so-called "DC Madam" who ran the escort service, Deborah Jeane Palfrey, was found dead two weeks after her April 15 conviction on all counts, including racketeering, money laundering and conspiracy.

Vitter's telephone number was discovered in her phone records. He apologized publicly for having committed a "serious sin" in his past. Palfrey had not yet been sentenced.

CREW said the dismissal of the complaint was in line with the committee's "standard operating procedure."

"While Deborah Jeane Palfrey, who committed suicide last week, was found guilty of operating a prostitution ring, Sen. Vitter has not been held accountable for his activities. He walks away without even a slap on the wrist," the group said in a statement.

(Reporting by Thomas Ferraro; Editing by Eric Walsh)