A five-year-old boy spent his fifth birthday party mourning the loss of his beloved dog after it was shot and killed with an assault rifle by an Oklahoma police officer - despite it being on the other side of a fence.

Eli Malone and several other children had gone inside for birthday cake on Saturday when they heard a loud bang, looked out the window and saw his dog Opie bleeding on the ground.

Eli's mother, Vickie Malone, said her son then cried to her saying, 'there's something wrong with Opie.'

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A five-year-old boy is still mourning the loss of his best friend after his family's beloved dog (shown after the shooting) was shot and killed by an Oklahoma police officer with an assault rifle during his birthday party

An emotional Eli Malone is still grieving the loss of his dog Opie. The three-year-old American Bulldog Pit Bull mix was shot by a Wynnewood police officer on Saturday during his party

Beloved dog Opie was shot dead during Eli Malone's birthday party

At the time of the shooting, the officer was serving a warrant for a man named Shon McNiel from a 10-year-old case listing the family's house (shown above) as the suspect's last known address

The adults at the home ran outside near where the fence surrounds the family's yard and found the three-year-old American Bulldog Pit Bull mix 'kicking and gasping for air,' according to FOX 25.

The officer, identified by family members as Wynnewood police officer Josh Franklin, used a high-powered rifle he got from his car to put the 90-pound dog down, the station reported.

As the children looked on from the window, the officer, who Malone said showed no remorse, reportedly fired two more shots from the rifle.

Malone's son and Opie's owner, Rio Youngblood, said he asked the officer, 'Why'd you shoot my dog?' the New York Daily News reported.

'He walks slowly out to his car gets an AR-15 and points it at the dog and pulls the trigger,' Youngblood told the Daily News.

'He fires another round and it ended my dog's life. He lowered his head and drove off.'

The dog then lied on the ground covered by a towel for more than an hour before another officer arrived at the scene to collect statements from the family.

'The kids were all watching through the window,' Malone told the Daily News.

The officer initially told the family the dog tried to attack him through the fence but did not offer any other reason for the shooting, according to the family.

Wynnewood Police Chief Ken Moore told the station the the dog charged the officer and that the shooting was justified.

Moore described the dog as vicious and said it attacked the officer coming around the corner of the house, according to FOX 25.

Vickie Malone, Eli's mother, (shown above) said after hearing a loud bang, the adults ran outside near where the fence surrounds the family's yard and found Opie 'kicking and gasping for air'

The officer, identified by family members as Wynnewood police officer Josh Franklin, used a high-powered rifled he got from his car to put the 90-pound dog down

The officer reportedly told the family the dog tried to attack him through the fence but did not offer any other reason for the shooting. Wynnewood Police Chief Ken Moore told the station the the dog charged the officer and that the shooting was justified

Video courtesy: KOKH

However, video footage following the shooting shows Opie lying on the ground near the fence, not the house, with his head surrounded by blood.

'The dog cannot jump the fence,' Malone told the Daily News. 'The gates to our yard are tied with wire and shoe string.

'The dog could maybe have gotten his head through the fence but he wouldn't have been able to open it.'

Moore noted he had not seen the video footage and said that before the officer shot the dog, the officer had tried to once kick it off of him.

At the time of the shooting, the officer was serving a warrant for a man named Shon McNiel from a 10-year-old case, listing Malone's house as the suspect's last known address, according to FOX 25.

The family said the officer did not show them a warrant after he told them he shot Opie.

'He said that he was looking for Shon McNiel,' Malone told the Daily News.

'I said, "There's no one here named Shon McNiel. Who the hell is Shon McNiel?"'

Following the ordeal, the family is still grieving the loss of their dog with Malone noting the incident has left some of the party's youngest guests not wanting to go outside to play anymore

Eli stands above with a marker at a memorial made in honor of Opie

Moore said at the time the officer was serving a warrant which gave him legal authority to be on private property.

Court records indicate McNiel's last known address was not Malone's house but instead a home on a nearby street, according to FOX 25.

Malone and her children have lived at the house for a year and told Fox 25 the officer who shot Opie had previously responded to calls at their address in the last year, and was aware of the dog.

'Officer Franklin had been to the house twice before,' Youngblood, who described the dog as 'amazing with kids' told the Daily News.

'Opie was chained on the front porch. They knew Opie was here, too.'

Following the ordeal, the family is still grieving the loss of their dog with Malone noting the incident has left some of the party's youngest guests not wanting to go outside to play anymore.

Youngblood said his son Vrylend is also still grieving Opie's death.

'I came outside last night and he's on the trampoline. He said, "I'm singing to Opie's heart. I miss him,"' Youngblood told the Daily News.

Meanwhile, the family is still waiting for an explanation and apology from the police department.