By Brian Maass and Mark Ackerman

ELBERT COUNTY, Colo. (CBS4)– The police use of a Taser on a man in Elbert County in April is now being listed as one of the causes of his death, according to a CBS4 Investigation.

“It was horrifying, it was obviously very traumatic,” said Elaine Holt, a friend of Matt Poer, who died April 12 immediately after deputies deployed a Taser on the Army veteran.

Poer, 46, had served in the Green Berets in both Afghanistan and Iraq, according to his family. But they say after he returned from his service, he exhibited signs of post-traumatic stress disorder or PTSD.

“After he came back from Iraq, we did notice a change in Matt,” said his mother, Sherry Poer. “I think a piece of his heart went every time someone was killed and it chipped away at his soul.”

His family said Matt Poer had a service dog, Dano, to help with his PTSD. But after that German Shepherd died, he came to Colorado to get another dog. He found Elaine Holt, who breeds and trains service dogs in Elbert County.

Holt called Poer, ”A very nice man and we became friends very quickly. Just a very nice person who loved dogs and needed a dog.”

Poer moved in to Holt’s property in rural Elbert County in March. She said life was normal until she returned to her home the morning of April 12.

“He said the property is under surveillance, there are cameras, the house is tapped. It caught me completely off guard,” said Holt.

She said Poer insisted there were strangers on the property, hiding inside a parked RV. She said she went with Poer to check out the RV but there was nobody inside.

“I started to just think something very strange is going on”.

Holt relayed that Poer then called the Elbert County Sheriff seeking help. She says he told them there were cameras on the property and he wanted police to respond. He apparently left a message and sometime later a sergeant called back and left a message, ”You called regarding some issues with a camera, give me a call back at the sheriff’s office.”

When there was no immediate response, Holt says Poer became more agitated and called 911. During that call, Holt said Poer handed the phone to her and retrieved her SIG Sauer pistol and walked away.

“At that point I’m on the phone with 911,” said Holt, ”I’m saying, ‘He’s having a PTSD episode.’ I said, ‘He’s armed, he thinks there is something going on, on the property.’ It was frightening at that point. Something was really wrong here.”

She said Poer paced around with the gun but she did not feel in danger. Eventually, he left Holt’s property and crossed a county road into some neighboring fields.

Mackenzie Gannon lives in an RV near the fields where Poer was walking.

She said, “We see a guy walking down the fence line, kind of waving a gun around.”

She said in short order, she and her boyfriend heard several shots as Poer apparently fired randomly into the unpopulated countryside. The couple also called 911. She continued to watch Poer who she said laid down in the grass appearing to be hiding.

Police arrived and Gannon said she was able to see and hear deputies shout orders at Poer, “Get down, get down, put your hands up, show us your hands, shut the F—up.”

From her perspective, she said she believed Poer was laying on the ground the whole time.

“He was on the ground. I don’t think he ever got up from the position he was laying down in. He was laying down in the grass clearly looking like he was hiding from something.”

It’s unclear at this point what happened to the pistol he had been carrying. But when the incident ended, Gannon said investigators peppered her with questions about the gun.

”Did you see him drop it anywhere?” she recalls being asked. “Because I guess the guy didn’t have the gun at the time they found him.”

What happened next in the field is unclear, as authorities have not released body camera footage or detailed the incident. But at least one Elbert County deputy deployed his Taser, hitting Poer in the lower back, according to the autopsy report.

“Taser deployment can be heard, followed immediately by a groaning sound by the subject and immediate unresponsiveness, from which he never regains consciousness,” wrote the coroner’s office. His manner of death is listed as homicide.

The coroner goes on to write, “It is my opinion that Christopher (Matt) Poer, a 46-year-old White male, died as a result of sudden death associated with amphetamine intoxication, dilated cardiomyopathy, and Taser deployment.”

The coroner said Poer’s body had a “toxic-lethal blood level of amphetamine,” indications of heart disease and a history of hypertension, obesity, chronic alcohol abuse, chronic kidney disease and congestive heart failure.

During the second call to police, Holt told dispatchers that Poer was not drunk or under the influence of drugs. A review of radio traffic from that night shows that information was relayed to officers.

Holt did say that Poer took two of her Adderall pills, which is classified as an amphetamine, but, “certainly not a lethal dose.”

Elbert County Sheriff Shayne Heap told CBS4 he could not comment on the case as an investigation is being conducted by the 18th Judicial District Critical Response.

In response to a query from CBS4, Heap said, ”No deputies were placed on administrative or any other type of leave as a result of this incident.”

Immediately after the incident, the sheriff’s office released information saying a deputy “deployed a Taser against a man at the scene who had a gun.”

That information was repeated by the district attorney’s office. DA spokesperson Vikki Migoya declined to discuss the accuracy of the statement simply saying, “That was the information at the time.”

Poer’s parents say they have received little information on what happened to their son. But, they say an Elbert county investigator told them,”That he was not armed.”

“This is not making sense, this is not adding up,” said Poer’s mother, Sherry. “You do not Taser an unarmed man.”

She and her husband, Doug, say they hope the body camera video will help reveal how their son died.

“I have questions about the entire evening,” said Doug Poer. “We want to know what happened and why is he dead?”

Matt Poer will be buried Aug. 11 at Arlington National Cemetery.

CBS4 Investigator Brian Maass has been with the station more than 30 years uncovering waste, fraud and corruption. Follow him on Twitter @Briancbs4.

Mark Ackerman is a Special Projects Producer at CBS4. Follow him on Twitter @ackermanmark