(CNN) -- The FBI is analyzing an audio recording that might give more clues about Michael Brown's shooting.
Federal investigators have obtained the audio and are questioning the man who says he inadvertently recorded audio of gunfire at the time Brown was shot by Ferguson, Missouri, police on August 9, the man's attorney told CNN.
It could be the newest piece in the larger puzzle of exactly what happened in the moments before the 18-year-old's death.
The man, who wants to remain anonymous, was talking to someone on a video chat service and happened to record the conversation, his attorney Lopa Blumenthal said. A quick series of shots can be heard on the recording, followed by a pause and then another quick succession of shots.
"At the time he didn't even realize the import of what he was hearing until afterwards and it just happened to have captured 12 seconds of what transpired outside of his building," said Blumenthal.
The man lives near the site of the shooting and was close enough to have heard the gunshots, she said.
Forensic audio expert Paul Ginsberg analyzed the recording and said he detected at least 10 gunshots -- a cluster of six, followed by four.
"I was very concerned about that pause ... because it's not just the number of gunshots, it's how they're fired," Blumenthal told CNN's Don Lemon. "And that has a huge relevance on how this case might finally end up."
She said she learned of the recording late last week from a mutual friend.
"I had to get his consent before I could reach out to the FBI," Blumenthal said.
CNN cannot independently verify the authenticity of the tape and has asked the FBI for confirmation of their interview with the man who made the recording.
The meaning of the pause
It's difficult to prove from the audio why the pause took place or whose narrative it supports.
Attorney Chris Chestnut said he was surprised by the gap in shots.
"It's the pause that gives most concern in a police shooting, especially with an unarmed victim, because at this point Mr. Brown is defenseless -- he has no weapon," said Chestnut, who represented the family of Jonathan Ferrell.
Like Brown, Ferrell was an unarmed African-American man who was shot and killed by a white police officer.
But if the gunfire heard on the audio is indeed from the Brown incident, the pause doesn't automatically suggest wrongful intent by the officer.
"To be fair, there could be other explanations for that pause," said attorney Van Jones, co-host of CNN's "Crossfire." "Maybe the officer will say, 'Well, I fired and he kept advancing, so I fired again.' "
Witnesses and a friend of Officer Darren Wilson have given conflicting accounts of what led up to Brown's death.
Dorian Johnson, who was walking with Brown at the time of the shooting, said the officer shot Brown once by the police car and again as he ran away.
According to Johnson, Brown was struck in the back and then turned around and put his arms up as the officer kept shooting.
But a woman who identified herself as a friend of Wilson called in to a St. Louis radio show last week with what she said was the officer's version of events. The caller, who identified herself only as "Josie," said Brown taunted the officer and charged at him. Her account matches what Wilson has told investigators, a source with detailed knowledge of the investigation told CNN.
An autopsy showed Brown had six gunshot wounds, all in the front of his body.
Key witness speaks out
Ferguson police said Brown allegedly robbed a convenience store shortly before the shooting.
And reports that his friend Johnson had a criminal record that includes lying to police has put Johnson's credibility in question.
In 2011, Johnson was arrested and accused of theft and lying to police about his first name, age and address.
Johnson said Monday night he doesn't understand why some are questioning his credibility.
"I see they bring up my past, my history, but it's not like it's a long rap sheet," Johnson told Lemon. "This one incident shouldn't make me a bad person."
CNN's Eliott C. McLaughlin, Tina Burnside, Julian Cummings and Greg Botelho contributed to this report.