Anderson isn't the only suspect being watched. The IRS has a court-ordered tap on Victor Conte's e-mail. BALCO's founder corresponds with an A-list of international sports stars and coaches who are surprisingly transparent about their involvement with performance-enhancing drugs. Some professional athletes ask Conte relatively straightforward questions about supplements but then suddenly turn secretive. Romanowski openly e-mails Conte about his vitamins. "Then it would get vague," says an agent. "He'd shift gears." Some of the players use single letters such as L, C and S as substitutes for drug names.

The e-mail contains rumors about new doping tests in track and field. In one e-mail to an elite track coach, Conte lays out how testers caught wind of athletes cheating with norbolethone, a never-marketed steroid from the 1960s. Conte tells the coach not to worry: "We already have a new one we're working on that should be available in a couple of months." Conte's communications to track stars and coaches include schedules for when athletes should take certain substances. Conte and the athletes speak of cream, a traditional steroid rubbed on muscles and joints, and a liquid drug called clear. In an e-mail to a top track athlete Conte declares, "Cream is the safest form to use, because it will not cause a spike in the testosterone level." Chances are that Conte's cream is cut with a masking agent called epitestosterone. Dr. Catlin informs Novitzky that sports dopers often take epitestosterone right before a drug test.

As White grows closer to Anderson, Novitzky continues his late-night trash runs. In the back alley behind the small BALCO offices, located in a commercial strip 100 yards from Bay Area Fitness, he opens a big green Dumpster with his gloved hands, swipes the trash and drives away to scour his take. From among the soiled lunch remains he pulls out papers indicating that Conte is shipping more than mineral supplements. Though routine ZMA supplements are mailed to athletes such as Romanowski at their home addresses and under their real names, other packages go out to players via Fed Ex under colorful pseudonyms.

Novitzky also issues a subpoena for the medical waste pickup from BALCO Labs. Several loads of medical castoffs reveal a treasure trove: dozens of used syringes containing clear, oily substances; vials of nutropin, a human growth hormone; and vials of epogen and epocrit, drugs favored by cyclists and long-distance runners to improve endurance.

The forensics lab at the San Mateo County sheriff 's office tests the syringes and quickly identifies traditional steroids such as testosterone and stanozolol. The testers are stumped by three or four other samples, though.

One day Novitzky scores a revealing piece of paper. "A blood test was done at an outside laboratory, Quest Diagnostics in L.A.," alleges White. "It was labeled B. BONDS." Shortly thereafter investigators retrieve correspondence from BALCO to the lab about a reputed error. The notice explains how B. Bonds's blood-test results should have been labeled as Greg Anderson's.

When Novitzky shares his find with the undercover men at one of their periodic meetings, they laugh in triumph. Now why would BALCO want Bonds's blood work changed to Anderson's?

By May White is part of the gym's inner circle, and the undercover cop is facing the physical test of his life. The third member of his training group is a six-foot-seven behemoth of a college lineman. Anderson is deadly serious about lifting, and if White wants to get to Bonds, he's going to have to keep pace with the big boys.

Anderson does his reps, grunting and breathing, and then they follow along. It's nonstop, except every once in a while Anderson's cell phone rings and he steps a good 15 feet away. From the trainer's body language it's clear these are business calls.

Even this close to Anderson, White finds it hard to guess his bulk. He knows he's bull-strong, but his long sleeves and sweats mask his build.

"Do me a favor," Anderson says to White one day after finishing a lift.

"Yeah?"

"Get rid of your short sleeves."

White understands. Old-school bodybuilders don't let others see how ripped they're becoming in the gym.

The role Anderson and the gym play in the BALCO scheme gradually becomes clear. Anderson doesn't just run a business by phone; elite international athletes come to the gym. One afternoon in the cafe White notices a black man with an imperious attitude and a British accent conferring with Anderson. Later White's fellow agents say the man is Dwain Chambers, the European 100-meter champion, here from Britain to train with Remi Korchemny, a Russian coach with ties to Conte. For all Chambers's visits, White never sees him work out.

Little by little Anderson opens up to White, who catches everything on his wire. Soon he confides how he trains several major league players. White casually asks how he can train so many different athletes during the day, and Anderson replies that he often counsels them "over the phone." Those words, White knows, could be the legal basis to support an application for a wiretap.

Agents keep Anderson under a microscope. White tracks him in the gym; when he leaves, drug agents and Novitzky have him under surveillance. Mostly he's a gym rat, but the agents tail him on his frequent forays to Pac Bell Park and notice that he is waved into the secured players' parking lot -- often for just a 30- to 45-minute visit. When Bonds is at bat, Anderson can often be seen in the tunnel behind home plate.