The man thought to have killed his estranged wife and two children on Christmas is a well-known vegan chef, author and motivational speaker who suffered from depression but recently turned his life around.

Police said Tuesday that Anthony Milan Ross was arrested late Monday night after exchanging gunfire with officers following a six-hour standoff in a Phoenix, Arizona apartment complex, according to AZ Central.

The 45-year-old has been charged with three counts of first-degree murder and more than a dozen counts of aggravated assault on an officer. He wasn't hurt in the police standoff.

Witnesses told police they saw him shoot his estranged wife Iris Ross as she tried to run away from him.

Then when they asked if she was fine, he said 'no' and pointed his gun at them before entering his apartment, where witnesses said they heard two or three more gunshots, according to police.

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Anthony Milan Ross, who is suspected of killing his estranged wife and two children on Christmas is a vegan chef and motivational speaker who recently turned his life around, according to police

The 45-year-old has been charged with three counts of first-degree murder and more than a dozen counts of aggravated assault on an officer. He wasn't hurt in the police standoff. Pictured are Nigel, 11, Iris, 38, and Anora, 10 months old, who were all killed in Monday's tragedy

Police found the bodies of all three in a Phoenix apartment complex. They found the wife lying outside an apartment, and when they tried to enter to see if the children were still alive began a six-hour standoff with Ross

He posted a video to Facebook on Christmas Eve in which he's singing with his 11-year-old son Nigel, the day before he allegedly shot the boy dead alongside his sister and mother

On Christmas afternoon Ross posted a touching video alongside his 11-year-old son, Nigel, singing 'Santa Claus is Coming to Town.'

Just 90 minutes later police said the shooting rampage began.

Ross's social media fans have reacted with shock by the disturbing news, as hundreds of his fans commented their horror on the video, which remains on his page.

Police responded to the apartment at around 4pm on Monday afternoon, finding Iris's body outside an apartment in the complex.

When police began to enter the apartment a standoff with Ross ensued.

Ross, who was commonly known by Milan by his fans, lost a significant amount of weight in his 20s when he switched to a vegan lifestyle.

He then became a chef and started writing and doing inspirational videos about his transformation and new lifestyle.

Ross was also featured alongside celebrities such as James Cameron and Samuel L Jackson in a feature-length documentary about veganism.

His Facebook profile more than 6,200 followers as of Tuesday night, though it seems that number may have dwindled throughout the day as news of the tragedy spread.

However, Ross was also battling depression, according to Iris's sister Mary Wogas.

'I received a text yesterday around 2.52pm,' Wogas told ABC 15, explaining that the texts came from her former brother-in-law.

'Two messages, first one saying "I just killed Iris and the kids. The second message was "with a gun." I knew that man was very unstable. I knew he had a very, very dark side. I didn't know it was this dark.'

Ross, who was commonly known by Milan by his fans, lost a significant amount of weight in his 20s when he switched to a vegan lifestyle

He then became a chef and started writing and doing inspirational videos about his transformation and new lifestyle

Howard said Ross lived in a different town and was in Phoenix visiting the children for Christmas. It's still not clear the motive for the killings

Tuesday morning police confirmed Ross as the father of the two dead children and that he and Iris were an estranged couple.

After finding Iris's body and confronting Ross, they negotiated with him for hours in a standoff, hoping that one or both of them were still alive.

He eventually told them that he'd killed the children, according to Sgt. Jonathan Howard, but not until after he'd changed his stories and said they were alive and threatened to kill them if police didn't leave him.

After several hours the Special Assignments Unit sent a robot into the apartment and it became apparent that the infant, Anora, was dead.

'Throughout the negotiations, he made comments that he had killed the children. He made some notifications to some family members that he had killed the children,' Howard said.

At around 7:30pm they also shut off power before going into the apartment while fending off gunfire from the suspect.

A few minutes later in a different room they found Nigel's body.

Ross surrendered to officers Monday night (scene above) after the killings and a subsequent shootout with police at an apartment complex. He wasn't hurt. An officer was injured by shrapnel and hospitalized in stable condition

Ross and Iris were involved in divorce proceedings, according to court records

Howard said Ross lived in a different town and was in Phoenix visiting the children for Christmas. It's still not clear the motive for the killings.

In the exchange of fire one officer, a 46-year-old on the force for 23 years was injured by shrapnel and taken to the hospital in a stable condition.

Ross and Iris were involved in divorce proceedings after Iris filed the papers in June, according to court records.

It's unclear if Ross has a lawyer who can speak on his behalf.