ATLANTA - The parents of a Florida man who died after Georgia sheriff's deputies repeatedly used stun guns on him said Wednesday they are very disappointed in a prosecutor's decision not to seek charges.

Chase Sherman's mother called 911 on Nov. 20 as they travelled on Interstate 85 from the Atlanta airport to their home in Destin, Florida. She said her 32-year-old son was "freaking out" and had taken a synthetic drug known as spice.

Video from the body cameras worn by Coweta County sheriff's deputies shows the deputies struggling with Sherman in the back of an SUV until he's still and they later realize he's not breathing. An emergency medical technician is seen in the video leaning on Sherman on the floor of the SUV and is heard saying he has Sherman pinned down.

Sherman was later pronounced dead at a hospital.

Coweta County Sheriff's Office records show that one deputy's stun gun was used nine times in a 2- 1/2-minute span for a total of 47 seconds, including one use that lasted 17 seconds. The other deputy's stun gun was used six times in just over four minutes for a total of 29 seconds.

Sherman's death certificate lists his death as a homicide and the cause as "sudden death during an altercation with law enforcement with several trigger pulls of an electronic control device, prone positioning on the floor of a motor vehicle and compression of the torso by the body weight of another individual."

Coweta Judicial Circuit District Attorney Peter Skandalakis on Monday announced that no charges would be filed in the case, saying that although Chase Sherman's death was tragic, it was not a criminal matter.

Sherman's parents said that they're angry and disappointed that the district attorney didn't think charges were appropriate even after having seen the video.

"We're disappointed he didn't even take it to the grand jury and let them decide," Mary Ann Sherman said.

Sherman's father, Kevin Sherman, called the district attorney a coward.

Chris Stewart, an attorney for Sherman's parents, said he plans to file a lawsuit and is calling on the U.S. Department of Justice Civil Rights Division and federal prosecutors in Atlanta to investigate the case.

After deciding not to pursue charges, the district attorney handed over his own investigative file and that of the Georgia Bureau of Investigation.

"In all of the cases that I've ever handled like this, this is the worst investigation I've ever seen," Stewart said.

He said that in their initial reports, the officers lied about the number of times they used their stun guns and that GBI investigators never pushed them on that when stun gun records showed inconsistencies. He also faulted the GBI for not talking to Sherman's parents and girlfriend until he made a fuss about it even though they were the only eyewitnesses there other than law enforcement.

A GBI spokeswoman did not immediately respond to an email Wednesday afternoon seeking comment on Stewart's criticisms.

News from © The Associated Press, 2016