(CNN) -- The grand jury in the case of Michael Brown's shooting didn't just face an onslaught of witnesses with conflicting memories of what happened the day white police officer Darren Wilson killed Brown, an unarmed black teenager. It also heard from witnesses who couldn't be believed at all.

Some admitted lying. Others changed their stories under questioning. Prosecutors were so skeptical of one woman's account that they asked whether she might have dreamed about seeing the confrontation in Ferguson, Missouri, on August 9.

Most of the dozens of witnesses who testified likely did their best to describe what they saw, but a review of thousands of pages of grand jury documents shows that untrustworthy testimony came from some witnesses on both sides.

"It's no surprise that some people did not tell the truth in this or any other grand jury," says CNN legal analyst Jeffrey Toobin.

What is unusual in the Ferguson case is that prosecutors chose to call so many witnesses, including some whose credibility they doubted.

"Usually, a prosecutor applies her own screen to the witnesses -- and only introduces evidence that she believes will be credible and believable," says Toobin.

Analysts differ over why prosecutors called witnesses with questionable credibility. Some say the prosecution wanted to present a jumbled case, to help Wilson. Others say the intense scrutiny and likelihood of a separate federal probe make it common in some places to toss anything and everything at a grand jury probing a controversial police killing -- even witnesses who prosecutors believe aren't likely to tell the truth.

Documents from the Ferguson grand jury

CNN's examination of thousands of pages of grand jury documents turned up several examples of testimony that came with little to no credibility. Here's a look at some examples:

Witness admits false statements

Witness 35 said Brown was "on his knees" when Wilson shot him in the head.

Under questioning, however, his testimony fell apart.

"What you are saying you saw isn't forensically possible based on the evidence," a prosecutor said.

The witness acknowledged making up testimony.

"Are you telling us that the only thing that's true about all of your statements before this is that you saw that police officer shoot him at point blank range?" a grand juror asked

"Yes," he answered.

Witness' racist rant: 'They need to kill the f-ing n-----s'

Witness 40's testimony supported Wilson's version of events. Yet prosecutors questioned whether she was even in Ferguson on the day Brown was killed -- and they asked her about a racist post online that would diminish her credibility as an impartial witness.

Video from that day shows no sign that her car was there, and the way she claims she drove home is physically impossible, authorities told her.

In later testimony, Witness 40 changed her story about some of what she saw and admitted to having gathered some details from news reports. She also gave a different reason for having allegedly been in Ferguson that day, and shared part of a journal that she claimed to have kept.

On the day of the killing, she posted a comment online saying, "They need to kill the f---ing n-----s. It is like an ape fest," the grand jury documents say. (CNN is redacting the "f" and "n" words, but she used them in full.) She also organized a small group helping raise money for officers, including Wilson -- a group she said was created as a result of this incident.

She also said she is bipolar, takes medicine for migraines, and has memory problems.

"Is it possible, do you think, that you dreamed about this after it happened and it feels real to you that you were up there?" a prosecutor asked. The witness insisted she knew it was real.

Prosecutor: 'Did you see this at all?'

Prosecutors called Witness 22 to explain that she lied to investigators and never witnessed the incident.

"You gave two statements, were both of those statements true?" a prosecutor asked.

"No," she answered. "I just felt like I want to be part of something ... I didn't see what I told the FBI what (sic) I saw."

She said she was actually passing along what her boyfriend told her he saw.

Prosecutors also played the grand jury a 10-minute police interview with a man who claimed to have witnessed the shooting. Then they played a phone call in which the man admitted that he actually had not seen the incident.

Another witness insisted another officer was with Wilson at the time of the shooting. (By all other accounts, Wilson was the only officer present when he shot Brown).

This witness described having a clear view of what transpired despite there being a building between the witness' location and where the incident took place.

"We all know people can't see around corners, right?" the prosecutor asked.

Another witness -- number 37 -- testified to seeing events that are hard to believe. He said that during a confrontation at Wilson's vehicle, Wilson shot Brown point blank in the chest -- but that Brown did not fall over and was not clearly bleeding as he ran away.

The witness also gave differing accounts as to how many shots were fired.

"You told three different stories in the time we've been here today. So I want to know which one is really your memory or did you see this at all?" a prosecutor asked.

Witness 37 posed an intriguing question to the prosecutors.

"If none of my stuff is making any sense, like why do y'all keep contacting me?" the witness asked.

Prosecutors' strategy debated

We posed that question to CNN legal analysts. Why did prosecutors present evidence from witnesses with shaky credibility?

Sunny Hostin, a former federal prosecutor, believes the state wanted to avoid presenting a clear-cut case that would have led to an indictment. "Prosecutors generally present very streamlined cases to the grand jury," she says. "As a prosecutor you should not present witnesses in front of the grand jury that you wouldn't present at trial."

"The prosecutors didn't want to indict," Hostin says. "That's why they conducted it that way."

Mark O'Mara, a defense attorney, said St. Louis County County Prosecuting Attorney Robert McCulloch had a different reason to present so many people.

The chief prosecutor's goal was "to avoid the argument that he customized the presentation for a particular result -- even though he had to presume, as it turned out, that he would still be criticized for that," O'Mara said.

Paul Callan, former deputy chief of homicide in the Brooklyn District Attorney's Office, says grand jury practices vary across the country.

Some prosecutors "use grand juries to provide political cover for the dismissal of difficult and controversial cases which the prosecutor knows will be lost at trial due to weaknesses in the available evidence," Callan says. These cases may involve police or civilians, such as "a store owner who shoots a robber under somewhat questionable circumstances or a father who kills the rapist of his daughter when he should've relied on the police.

"McCulloch's approach in presenting virtually every shred of existing evidence to the grand jury is unusual but not unprecedented," Callan said.

Some prosecutors in New York, for example, present virtually all evidence to grand juries in cases of police shootings, Callan said, citing a former high-ranking fellow prosecutor from another office.

"Cop shooting cases are always highly controversial and there is an awareness that the omission of any evidence may subject the prosecutor to future public criticism by either the family of the victim or by the police officers involved," Callan said.

Also, "virtually all of these cases now result in subsequent civil litigation where the record of the prior investigation will be closely examined and possibly publicized."

Local prosecutors know that federal authorities might open an independent investigation -- as they have in Ferguson, Callan says. Federal investigators will obtain copies of the grand jury presentation and "an unfair or incomplete presentation may subject the prosecutor to criticism."

Analyst: Process, not necessarily result, is in question

As it is, prosecutors have hardly escaped criticism for throwing so much at the grand jury in Ferguson.

"I actually think the result -- no charges -- is defensible. But I don't think the process he (McCulloch) followed was appropriate," says Toobin, who also is a former prosecutor.

"The best thing the criminal justice system can do is treat everyone the same," he says. "And the process that the prosecutor used -- using a grand jury, which is rarely used in any kind of setting, and throwing all the evidence, rather than a selection of it, before the grand jury -- almost seemed to dictate the result, which was an exoneration."

Still, Toobin says, the evidence shows that a conviction would have been very unlikely had the case gone to trial.

"Given the evidence that came out, I think the exoneration may well be justified. But I don't think the process inspires a lot of confidence."

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CNN's Eve Bower, Amy Drake, Mayra Cuevas, and Amy Roberts contributed to this report.