The father of a victim of the Minneapolis shooting has branded the transgender gunman who took the life of his 8-year-old son a "coward".

Fletcher Merkel and a 10-year-old pupil were murdered after Robin Westman, 23, opened fire through stained-glass windows during school Mass at the Annunciation Church, also home to a Catholic school, on Wednesday.

Eighteen others, primarily students aged between six and 15 years old, were injured by the transgender killer during the violent attack.

Speaking at a press conference, Fletcher's father, Jessie Merkel, said: "Yesterday, a coward decided to take our eight-year-old son Fletcher away from us.

Fletcher Merkel and a 10-year-old pupil were murdered after Robin Westman, 23, opened fire through the stained glass windows during school Mass

"Because of their actions, we will never be allowed to hold him, talk to him, play with him, and watch him grow into the wonderful young man he was on the path to becoming.

"Fletcher loved his family, friends, fishing, cooking and any sport that he was allowed to play.

"While the hole in our hearts and lives will never be filled, I hope that in time, our family can find healing.

"We love you, Fletcher. You always be with us."

Officials at Hennepin County Medical Center confirmed on Thursday that nine people were still hospitalised, including a child who remains in critical condition

Officials at Hennepin County Medical Center confirmed on Thursday that nine people were still hospitalised, including a child who remains in critical condition.

Students who survived they attack have said they did so by hiding beneath church pews, running to the building's basement and even hiding themselves beneath other children until they no longer heard gunfire.

After Westman unloaded 116 rifle rounds, the killer died by suicide.

A motive behind the rampage has not yet been determined.

Students who survived they attack have said they did so by hiding beneath church pews, running to the building's basement and even hiding themselves beneath other children

The killer's journal has since been recovered by the authorities, who found harrowing early plans for the shooting.

It read: “I am feeling good about Annunciation. It seems like a good combo of easy attack form and devastating tragedy and I want to do more research.

"I have concerns about finding a large enough group. I want to avoid any parents, but pre- and post-school drop-off.

“Maybe I could attack an event at the on-site church. I think attacking a large group of kids coming in from recess is my best plan.

The killer's journal has since been recovered by the authorities who found harrowing early plans for the shooting

"Then from there I can go inside and kill, going for as long as I can."

The diary also documented how Westman felt "tired of being trans" and wished "I never brain-washed myself".

Authorities have said they have been unable to make contact with the shooter's mother, Mary Grace Westman, who worked at the school before retiring.

FBI Director Kash Patel said the agency was investigating the attack "as an act of domestic terrorism and hate crime targeting Catholics".