Nearly a month before they raided Tokyo Massage, investigators already suspected the business was taking steps to avoid detection, a federal report shows.

In the waning months of 2008, investigators went through the massage parlor's trash but did not find condoms, even though customers said they had used protection when visiting the brothel. Authorities also discovered that return and mailing addresses were routinely cut off of discarded envelopes, according to the report.

"Trash runs demonstrate that the people at Tokyo Massage are very savvy as it pertains to throwing items of evidentiary value in the trash," the document states.

The report, attached to a sworn statement by a legal assistant who worked on the case, offers new insight into the law enforcement investigation of the longtime Natrona County business. The effort culminated Jan. 7 when authorities shut down Tokyo Massage and arrested four suspected employees.

Since then, three employees and a number of johns have been convicted of various prostitution-related crimes.

The report, penned by an agent with U.S. Immigration and Customs Enforcement in mid-December, was part of the evidence prosecutors turned over to lawyers for the defendants. It became public after an evidentiary dispute between the Natrona County District Attorney's Office and Doug Hendrickson, the lawyer for Tokyo Massage madam Kyong Stodolka.

Last week, Hendrickson's legal assistant wrote an affidavit in connection with the dispute. The report was attached to that document.

By Dec. 17, the date of the federal report, federal authorities had already been conducting surveillance of Tokyo Massage for roughly two months, the document states. Officers has stopped several people for traffic violations after they were seen leaving the business. Some had indicated they paid for sex at the parlor.

Investigators had also identified Stodolka as the person running Tokyo Massage. They had also been in contact with law enforcement officials from Minneapolis, who suspected Stodolka had been the madam of a brothel there called Yoshiko's Sauna.

A retired Minneapolis police officer told local investigators Stodolka always separated the johns from their clothing before propositioning them and got rid of used condoms by dumping them in the trash cans of other businesses, according to the report.

Similar allegations have been made about the operation at Tokyo Massage.

Stodolka is serving a six-month jail sentence for promoting prostitution at Tokyo Massage. At her sentencing, Hendrickson noted his client has never been arrested or charged in connection with the Minnesota allegations.

Ken Robertson, another of the Tokyo Massage defendants, is also mentioned in the report. Investigators observed him buying food and supplies from Wal-Mart, running errands and bringing take-out food to the massage parlor.

Robertson pleaded guilty to conspiring to promote prostitution and was sentenced to probation.

One Tokyo Massage defendant who is not mentioned in the affidavit is June Wilhelmi. She is charged with prostitution and promoting prostitution, and is due in Natrona County District Court this morning for her arraignment.

Reach crime reporter Joshua Wolfson at (307) 266-0582 or at josh.wolfson@trib.com. Read his blog at tribtown.trib.com/JoshuaWolfson/blog.