The Dallas Independent School District police detective who was the driving force behind the district's crackdown on "cheese" heroin is being investigated after accusations he brought a gun to interrogate a mentally retarded man and kept questioning him after the man requested an attorney.

The detective, Jeremy Liebbe, remains on duty, but Dallas County prosecutors dismissed two aggravated robbery charges against the man, Mario Wright, because an audio recording revealed Liebbe ignored his request for an attorney.

Wright's attorney, Bill Wirskye, contends the recording also captures the sound of Liebbe pulling back the slide on his semi-automatic pistol as he threatened Wright.

Liebbe, who said he is cooperating with the DISD probe, said he acted properly and would never bring a gun to an interrogation. He said prosecutors were wrong to drop the charges.

"The allegations that have been lodged against me are baseless," Liebbe said.

DISD officials declined to comment, citing personnel issues and its ongoing investigation. Dallas County prosecutor Kevin Brooks said the office is not investigating the alleged gun incident because the charges against Wright were dropped.

But Wirskye, a former prosecutor, said Liebbe's actions are so egregious that he should no longer be a police officer.

"He never needs to investigate a violent crime again. He doesn't know what he's doing," he said. "The gun in the confession room, he ought to lose his badge for that, frankly."

Wright, 22, functions at about the sixth-grade level, his family said.

He completed deferred adjudication probation on two misdemeanor marijuana charges in 2006 and 2007. In both cases, a judge ruled "no finding of guilt," and they are not convictions.

Records show he suffers from major depressive order. Wirskye said Wright used marijuana to self-medicate his depression.

Wright said he doesn't understand what happened on Nov. 30, 2007. His family said he took a bus to a skating rink on East Ledbetter Drive to test whether he could go out on his own. Just before 8 p.m. – about the same time Wright said he was on the bus – two men were robbed.

First, three men and three women robbed a custodian at Pease Elementary, not far from the Oak Cliff skating rink. After handing over his wedding ring and other items, the custodian ran inside. One robber fired a shot and the bullet struck a door.

Minutes later, several men and women robbed a man at a bus stop on East Ledbetter. The victim said he followed Wright to the rink.

Wright said that he had skated around the rink once when he saw a man pointing him out to police. He was identified by other witnesses and taken to the Dallas police southwest substation.

Prosecutors say Wright told Dallas police that he wanted a lawyer, so officers didn't question him. Liebbe, the on-call detective for DISD, was called to come to the station because of the robbery at Pease.

About four minutes into an audio recording of Liebbe's interrogation, there's a sound that Wright and Wirskye said is Liebbe pulling back the slide on a gun. There is no video.

"I remember this detective pulled out a handgun and showed it to me," Wright later swore in an affidavit. "He was messing with the gun and it made a click-click sound when he pulled the top part back. He also showed me a bullet that was in a plastic bag."

Liebbe said the sound is the rattling of a jar containing the recovered bullet and shell casing from the school robbery.

"What you hear is me pulling that jar out of my jacket and putting it on the table next to the recorder," Liebbe said. He said he could understand how those listening to the audio could be confused if they'd been told they would hear a gun.

Liebbe said he locked his gun in the desk of Dallas police Detective Madison Jacob, who investigated the other robbery. Jacob declined to discuss the case, but his supervisor, Sgt. Calvin Johnson, confirmed Liebbe's account. Johnson said Jacob did not watch Liebbe's interview.

Minutes after the unusual sound on the recording, Wright asked for an attorney.

"I wasn't involved in none of this," Wright says. "I can't get no lawyer?"

"You can get a lawyer, yeah. You have that right," Liebbe replies. "Didn't I explain to you that you have that right?"

"I want a lawyer," Wright says.

"It's a perfect recipe for injustice," Wirskye said. "You have a detective that presupposes guilt. ... He won't listen when he [Wright] asked for a lawyer and he pulls a gun out in the interrogation, and it led to a false confession."

A 1966 U.S. Supreme Court case, Miranda vs. Arizona, said if a suspect clearly requests a lawyer, questioning must stop, although the suspect can change his mind and reinitiate questioning.

Southern Methodist University law professor Jenia Turner said Wright's request for a lawyer was obvious. She said the fact that Wright kept talking did not alter his demand.

"'I want a lawyer' is pretty clear," Turner said. "It's pretty hard to argue that it's ambiguous."

But that's Liebbe's argument.

"As long as you keep talking," it's not a violation, Liebbe said. "I realized, yeah, I'm going into a gray area."

On the job, though, Liebbe won kudos for his work fighting "cheese" heroin. He investigates other crimes on school campuses but most notably investigates drug cases and has helped some children seek treatment. He wrote a bulletin in March 2006 that went to law enforcement throughout the country, alerting them about the cheap and often deadly concoction of black tar heroin and cold medicine.

David Alex, a Dallas County prosecutor who used Liebbe as a witness in a cheese case, said he would call him to testify again.

"He is not your traditional law enforcement guy," Alex said. "But he is meticulous about what he does. He broke the cheese deal in DISD and was able to put together an investigation that I think was very instrumental to keep it from spreading to other jurisdictions and other states."

But Wright sees a different Liebbe.

"I don't think he ought to work for the police company no more," said Wright. "He ought to find himself another job."