Heroin buyers are often concerned about the purity of their purchases. But most of them do not enlist the help of police officers to test it.

Last Thursday at about 5 a.m., Brian Tippy ’02, 22, brought a small bag of white powder he allegedly purchased on the corner of Whalley Avenue and Goffe Street to the Yale Police substation in Phelps Gate, Lt. Michael Patten said. Tippy announced that he had just purchased what he thought to be heroin and wanted to test its authenticity, police said.

The good news: The substance tested positive for heroin, Patten said.

The bad news: Tippy was immediately arrested for narcotics possession.

But Tippy said the Yale Police report is by no means the whole story of what happened that Thursday morning.

The former Whiffenpoof and current Teacher Preparation Program participant said he was arrested that morning but that some of the information in the police report was wrong.

“Something did happen,” Tippy said. “But those details aren’t accurate.”

To air his side of the story, Tippy hired William F. Dow III, a prominent local defense attorney.

Reached for comment late Monday night, Dow implied that Tippy’s goal in presenting the drugs to the police might have been to fight crime.

“The last place in the world that a person who intended to illegally possess drugs would go is to the police and ask them to test that substance,” Dow said. “Sometimes, people who are inexperienced and want to help out law enforcement don’t really understand how things work.”

Tippy’s roommate, Evan Leatherwood ’02, had a similar hypothesis.

“He probably tried to obtain evidence to give to police to catch the guy who sold him the drugs. He’s a boy scout,” Leatherwood said, referring to Tippy’s character.

Otherine Neisler, one of Tippy’s lecturers in the Teacher Preparation Program, expressed similar disbelief about the facts alleged by the Yale Police.

“I’ve never seen anything that would indicate that something like this is true,” she said.

Tippy, a humanities major, said he hopes to teach English at the high school level after graduation. He currently works at a school — not under the auspices of the Teacher Preparation Program — but would not give the name of the institution.

Dow also said an improper knowledge of the inner workings of law enforcement “can result in an arrest where a person never had any intent to commit a criminal act.”

“That’s what happened to Brian in this case,” he added.

Dow and Tippy are scheduled to present their case in court this Friday.