Mr Manning told Justice Denis Clifford and a jury of seven men and five women that Leota and Samoa were longer-term inmates who had been moved to Hawke's Bay Prison from Auckland.
Poi was a comparatively new arrival who, the Crown alleges, was enlisted by the two to organise bringing contraband into the prison.
The plan involved the pair's partners in Auckland obtaining methamphetamine, cannabis and tobacco, relaying it with nicotine patches to Poi's partner in Hawke's Bay and arranging for her and another woman to take the goods the jail on a family day.
But when the women neared the prison and saw other vehicles and arrivals being searched they "lost their nerve and the package got thrown out the window," Mr Manning said.
Thus the delivery did not take place and it was later in the afternoon, after families had left and prisoners were returning to their cells, that the attack took place with Mr Manning saying CCTV images showed Leota going into his cell, No 6 in Unit 8, with Mr Poi.
Mr Manning said there were immediate thumping and other noises from the cell and a few seconds later Samoa also entered the cell, and remained there for 29 minutes during which there were similar noises.
The Crown said another inmate entered the cell, found Mr Poi unconscious in a pool of blood, and freed his tongue to stop him choking, amid a discussion between Leota and Samoa as to what they were going to do.
It is alleged Leota started taking steps the Crown said were aimed at trying to conceal his involvement.
Prison staff had been unaware of the incident and learned of the injuries after Mr Poi had been removed from the cell. Mr Manning said it was an irony that when staff then locked-down the unit and inadvertently focused on another cell, it left Leota in his own cell and able to start clearing up the blood.
Defence counsel Bill Calver said in a short opening address said the defence was the Leota did not participate in the attack.
Justice Clifford told the jury the trial was expected to take up to a fortnight.