When officers finally rushed into the room the pair were using for a specially arranged visit, he slashed her throat four times, exposing her larynx, the prosecution said.
Nicholas Fryers, 28, had a two-hour supervised visit with the woman at Wormwood Scrubs. When a prison officer warned them time was up, Fryers rose and said he wanted to embrace the woman. "It was a cold and cynical exercise to get her close enough to attack her," Stephen Smyth, for the prosecution, said.
Fryers spun the woman round, holding a razor blade at her neck. He shouted for the door to be locked and the probation officer was taken outside leaving the pair alone. Fryers shouted several demands and kicked a chair to the door.
"A number of prison officers were looking in through the windows wondering what to do," Mr Smyth said.
The woman was instructed to lie on the floor and take her knickers off. She thought she was going to be killed and did what she was told. "As she lay on her side, he raped her, keeping the blade by her neck to enforce his demands."
Mr Smyth said that in normal circumstances where a man was armed, prison officers would have thought the reasonable thing to do was to talk the prisoner round. But they were faced with a rape.
A deputy governor arrived and it was agreed the incident had to be stopped. The door was unlocked and officers rushed into the room. "But before they reached him he did what he had threatened and cut her throat - fortunately missing the jugular vein."
The woman received three cuts to the front of her neck and one at the back, which was sewn up by the prison doctor.
When interviewed later, Fryers allegedly said: "I admit I had sex, but I asked her first," suggesting she consented, said Mr Smyth. Fryers has denied rape and wounding.
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