Brenda Brown was arrested for marijuana possession, but the arresting Baltimore police officer has pleaded guilty to charges he falsified information and made illegal arrests. (Kenneth K. Lam/Baltimore Sun video)

When Brenda Brown stood before a judge, she figured she had only one real option: plead guilty. She had been caught with three bags of marijuana in her pocket in Northwest Baltimore.

She didn't know that Kendell Richburg, the arresting officer, had lied about having seen her buy the drugs, potentially violating her constitutional right against unreasonable search and seizure. Now, her case is among hundreds under review by prosecutors in light of Richburg's conduct.

Brown, 52, is serving a sentence that includes a year of probation, court costs, counseling, drug testing and another possession count on a lengthy rap sheet. But she wonders whether the new revelations mean her conviction might be scrapped.

"You mean I'm off probation?" she asked after hearing of Richburg's guilty plea this month to armed drug trafficking charges. Federal prosecutors said the Baltimore police officer set up innocent people, falsified reports, skimmed police money, and protected a drug dealer working for him as an informant.

Brown's case — and others like it — are part of a complicated puzzle prosecutors will have to solve in coming weeks.

"This could be a very big undertaking the state's attorney's office will have to embark on," said Glenn F. Ivey, a private attorney who served as Prince George's County state's attorney for eight years. He said one police officer's misconduct can ruin many cases.

The Richburg affair has endangered cases against people caught engaging in criminal activity. And it illustrates how seemingly incidental, but fabricated, information can slip through the court system, limiting suspects' due process.

"Whether the person is guilty or not, the police have to put truthful information in the report about him or her," U.S. Attorney Rod J. Rosenstein said. "You don't make cases by lying."

Brown was arrested Sept. 18. That night, she said in an interview, a young man on a bike rode up to her at a bus stop in the 5100 block of Park Heights Ave.

"Hey mama, I got some weed but you got to look out," Brown said he told her. "Some knockers down there."

He pointed toward an area being monitored by plainclothes officers from Baltimore's Violent Crime Impact Section. Brown discreetly handed the man $15 for three "nickel" bags — enough to roll a joint, she said — and boarded a bus.

Several minutes later, she said, a police car pulled in front of the bus. Richburg stepped onboard and pulled Brown off.

"What you got?" she said he asked. "I know you have something."

He reached into her pocket, pulled out the baggies. She never questioned how he knew she was holding marijuana.

In the statement of probable cause for the arrest, Richburg wrote that he witnessed the buy. He said an "unidentified black male" in a white T-shirt and blue jeans approach Brown at the bus stop. Money changed hands, he said. "This detective believed that he had just witnessed a narcotic transaction," he wrote. He and his partner walked up and made the arrest.

There was no mention in the report of Richburg stopping the bus.

That wasn't the only omission. According to federal prosecutors, the entire arrest was set up. Earlier in the day, federal investigators, who by this time were monitoring Richburg, had been wiretapping his conversations with a confidential informant.

According to Richburg's lawyer, Warren A. Brown, the officer had been under immense pressure to make cases, which led him to arrange busts with the informant. That day, the two discussed the potential drug arrest.

"I'll write it up like I saw hand to hand," bits of the conversation made public by federal prosecutors show.

It was unclear whether the man on the bike was the informant. But after the drug deal was brokered, the informant gave Brenda Brown's description and location to Richburg, who texted back several minutes later: "I got her."