"I ran to the left. I got shot and I just fell to the ground."
Instead of fear, Boztas says he felt at peace with the fact he might die.
"I was just so calm. I was at the almighty God's house - that's the best place to die, to go to heaven."
He said he waited on the ground until the shooting stopped. He then smashed a window and run outside.
That's when he came across Mustafa.
Due to the location of the teen's injury, Boztas couldn't do CPR so instead tried to hold the wound.
"I started mouth-to-mouth but I couldn't save him and picked up the phone from the ground. I was talking to his mum and I said, 'I think he's dead. Please come to the mosque'.
"She couldn't believe it. She was saying, 'Is it my husband or my son?' I said, 'I think it's your son'.
"She was in shock. She was yelling and screaming and breaking down."
At that stage the shooting resumed.
Boztas said he closed Mustafa's eyes "for respect", dropped the phone and ran again.
He didn't get far before his leg "stopped responding" and he fell to the ground. A policeman eventually came to his aid and waited with him till paramedics arrived.
A week on and Boztas, who came to New Zealand from Turkey 10 years ago, remains in hospital unable to walk yet. The bullet travelled up his thigh and into his liver. A fragment remains lodged in a rib.
He was temporarily released from hospital today so he could attend the prayer session at Hagley Park and later the funerals for 26 victims, including 3-year-old Mucaad Ibrahim, the brother of his good friend.
Boztas said one of the most difficult parts of that day was seeing the young people who were injured and killed.
"You want to help them to live because they are young.
"The hardest part was for me not being able to save [Mustafa]."
He said the community had been "unreal". So had Prime Minister Jacinda Ardern, who visited him in hospital.
"She was really supportive, she was awesome. She gave me a hug and she just wished me well and to stay strong."
He said her visit left him in tears.
Like most of those who were injured or lost loved ones, Boztas said he wanted the shooting to unite people.
"I just want everyone to know Islam is not about terrorism, it's about love."