In the case of Raymond Jonassen, who was locked up for four months based on false information, the answer seems simple at first.

A county police detective wrote in court charging documents that fingerprints at a December burglary scene in Glen Burnie matched Mr. Jonassen's.

That was erroneous, and charges including burglary and theft were dropped May 29.

Clearly, Detective Gregory Tate is at fault, as documented in a front-page story in The Sunday Capital. But if you stop there, without asking what else might have gone wrong, you haven't learned much.

What about the court commissioner and judge who ordered Mr. Jonassen jailed, the prosecutors who proceeded with a case that turned out to be bogus, the Public Defender's Office that represented Mr. Jonassen?

They all might have done their jobs in this case, and a man still spent four months in jail. In a sense, then, the whole system is to blame.

Not a very satisfying answer, but then again real life so rarely offers an easy villain.

From the moment Mr. Jonassen was arrested Jan. 31, nine days after a warrant was issued, the system effectively assumed he was guilty, contrary to the judicial mantra we all know: "innocent until proven guilty."

It made sense: Mr. Jonassen, 23, has a history of theft convictions and drug charges. And to cope with clogged court dockets, the criminal justice system relies on an unspoken assumption that nearly everyone is guilty. Justice chugs forward, with innocent people sometimes caught in the gears.

You don't have to be a bleeding-heart liberal, mistrustful of police or sympathetic to criminals to wonder how many other Raymond Jonassens are out there.

"I don't know that it's running rampant in the system, but I don't think it's isolated, either," said William Davis, chief public defender for the county. "The system is not perfect, and there are holes."

The commissioner and judge who ordered him jailed were relying on sworn charging documents.

Prosecutors didn't assign an attorney to the case until almost two months after the arrest, a routine time lag. Serious cases generally go to trial four to six months after an arrest, at the earliest. And Assistant State's Attorney Crighton Chase, the prosecutor assigned to the case, naturally assumed what the detective wrote was true.

William Cooke, the public defender who represented Mr. Jonassen, was not assigned until April, which is also routine. Within weeks, Mr. Cooke obtained copies of the evidence against his client, known in the court system as "discovery," and quickly saw there was, in fact, no fingerprint match.

Of course, all of these people - police officers, commissioners, judges, prosecutors, defense lawyers - face a heavy caseload and have to rely on certain assumptions and shortcuts to do their jobs.

And while mistakes like this are troubling, they're rare and there's probably no way to prevent them entirely without slowing justice to a crawl, said Kristin Fleckenstein, a spokesman for State's Attorney Frank Weathersbee. Imagine, she said, if no one could be charged until police completed their investigation and the entire file had been reviewed by a prosecutor.

True, there's no easy answer. But it's frightening to think that one man's word - even a police officer's - can essentially go unchallenged for so long.

This mistake was caught. As Ms. Fleckenstein said: "The system of checks and balances did work in this case."

But how often does it not work?

Clearly, Detective Tate's statement was either a lie or a mistake. It's hard to believe the former. Would a 14-year veteran risk his pension, reputation and freedom by lying to close a minor burglary case in which nothing was taken, especially with a lie so easily disproved?

It's not impossible, though; a state police ballistics expert killed himself in 2007 after public defenders exposed the fact he had repeatedly lied under oath about his credentials, casting many convictions into doubt.

But Detective Tate, too, should be presumed innocent. Sgt. John Gilmer, a county police spokesman, told me yesterday the department is still in the "initial stages" of an investigation into what went wrong. He declined to say who in the department is conducting the investigation.

Citing personnel rules that protect officers, Sgt. Gilmer also declined to say whether Detective Tate is still on active duty.

The person who answered the phone yesterday at the Northern District station said Detective Tate was supposed to work yesterday; he did not respond to my voicemail.

Mr. Davis said he hopes police and prosecutors get to the bottom of what happened. His Public Defender's Office has been making inquiries, too.

"I'd like to know if this was a mistake. If so, how was the mistake made, and how can we make sure something like this doesn't happen again?" Mr. Davis said. "Or is it something more serious?"