Detectives use the tactic all the time: Call a suspect and ask him to drive to the station for an informal talk. The detectives get to ask their questions without having to warn the suspect of the right to remain silent.

But in Montgomery County, they’re pushing things too far, according to a judge who delivered a rare rebuke from the bench as he tossed out a confession in a rape case. Circuit Court Judge Eric M. Johnson ruled that police allowed a casual questioning to turn into a formal custodial interview that required the suspect to be read his rights, and he wasn’t.

“A system of subterfuge has developed in the law enforcement community with respect to interrogation techniques,” said Johnson, who in his ruling did not name other cases in which he thinks police have crossed a line.

What made the ruling noteworthy is that Johnson is a former Montgomery police officer who chats regularly with detectives and commanders — in courthouse hallways, in his chambers, in the middle of the night when they need to get a search warrant signed. But in the rape case, he aimed to make a broad point about constitutional protections.

“This message is sent,” he said from the bench last month.

In the wake of the ruling, the suspect was released from jail Thursday on the condition that he stay away from his teenage daughter, whom he’d admitted to fondling and having sex with over a three-year period when she was 11 to 14 years old, according to court records.

Prosecutors — who said the detectives acted appropriately — have moved to try to get Johnson’s ruling reversed by an appeals court, which could save the rape case and blunt Johnson’s ruling from spreading to other criminal cases. Police said the ruling should be reversed, and they worry that if more judges adopt Johnson’s thinking, it would limit what they see as a reasonable and valuable tool.

“I have no problem with what the detectives did,” said Montgomery Police Chief J. Thomas Manger. “I have confidence in my detectives as they work these cases.”

Local defense attorneys have mixed reactions to the ruling. Some played it down; others called it courageous and overdue.

“Detectives come as close to the line as they can,” said defense attorney David Felsen, “and in this case Judge Johnson said they crossed it.”

“It could be a huge benefit to us,” added Andrew Jezic, co-author of the book “Maryland Law of Confessions.”

At issue in the rape case was a legal battle prosecutors and defense attorneys often wage before cases ever get to juries: Was the suspect in “police custody”?

The battles typically turn on specific details: Did the suspect drive to the station? Was he ever handcuffed? Were detectives accommodating or belligerent? Was the suspect told he was free to leave? Was he allowed to go home?

Courts have determined that once a “reasonable person” believes he cannot leave, he is susceptible to intimidation — even when detectives are acting calm and unthreatening. At that point, for the interrogation to be admissible at trial, detectives generally must advise the suspect of his rights to remain silent and to speak to an attorney — a process known as giving suspects their Miranda rights.

“What is wrong with giving people their Miranda rights?” Johnson asked from the bench, invoking the thinking of detectives trying to make a case. “I’ll tell you what’s wrong with it: As soon as defendants are given their Miranda warnings, they often lawyer up. And when they lawyer up, [detectives] don’t get the information that the detectives want to get.”

The heart of this case started just before 6 p.m., Aug. 31, when detectives called the 34-year-old rape suspect and asked him to drive to the station. They had just spoken to his wife and 14-year-old daughter.

(The Washington Post typically does not identify victims of sexual assault. In this case, The Post also is withholding the suspect’s name to protect the victim’s privacy.)

The suspect, then a military sergeant still wearing his workday fatigues, arrived at the police department’s family crimes unit, where he was greeted by two unarmed, plainclothes detectives. They led him to a back area, using a key card to go through a door. They went through a second door into a small room, one typically used to speak with young witnesses. The door was closed behind them.

The suspect sat on a small sofa against the far wall. To his side was a bookshelf stuffed with teddy bears. The detectives sat on chairs across from him.

“Thank for you for coming in. It looks like we caught you coming in from work,” one of the detectives said, according to a video recording played in court. The detective spoke in a soft voice, even chuckling a little bit when she talked about being short.

“Okay. Well, again, I want to make sure you understand. This may not look like a police facility, but it is a police station. You’re not under arrest or anything like that, okay? This door is not locked. I’ll leave the door unlocked. And if I could reach it, I would open it for you. But I’m vertically challenged. But the door is unlocked, okay? So I just want to make sure you understand that.”

They began talking about his daughter.

He admitted to fondling his daughter, showing her pornography, taking pictures of her naked and having sex with her 10 to 20 times. The detectives suggested he write her a letter.

“I just want to say I’m sorry for all the wrong things I’ve done to you and made you do,” he wrote.

After a time, the man became despondent. The detectives asked whether he’d be okay if he left the station. “I don’t think so,” he said.

Detectives arrested him that night at the station without issuing him Miranda rights. Prosecutors argued in court that they never had to because he was never in custody. Detectives twice told him he wasn’t under arrest — once later in the interview — and moved to lock him up only after he admitted to a violent crime and indicated he was a danger to himself.

Before the man’s trial was scheduled to begin last month, defense attorney Michael Gambrill argued that no reasonable person would have believed he was free to leave. Gambrill noted the position of the chairs and sofa in the small interview room.

“He’s got to go through them to get out,” Gambrill said. “It ain’t happening.”

Johnson was quick to credit the detectives’ tone and motives: “They’re polite, they’re courteous, they’re respectful. . . . They wanted to get this guy for committing a horrible crime.”

But he zeroed in on two things: The detectives never explicitly told the man that he was free to leave, and after he began making admissions, he was never read his Miranda rights.

“In all my experience, I never had any suspect get up and walk out of the interrogation room, or even think that he could,” Johnson said. He added: “I don’t think any lawyer in this room really believes that a person can go in a police station and confess to a violent crime crime and say, ‘I’ll see you later.’ That just isn’t going to happen. It doesn’t happen in the real world. And the technique of doing that ought to be stopped.”