Sams, 53, attacked the probation officer, Julia Flack, 49, an archdeacon's wife, on Monday as she held a surgery in the prison. Sams was jailed two years ago for the murder of Julie Dart and the kidnap of an estate agent, Stephanie Slater.
The National Association of Probation Officers claimed that no one had told its workers that Sams had been transferred to the prison's B wing, where the incident took place.
Its assistant general secretary Harry Fletcher also claimed that there had been complaints that Sams had made a number of threats, mainly against female members of staff. The Prison Service is investigating the case.
The announcement came on the day that a Government report was published, revealing the results of a survey in which one-third of the Hertfordshire probation staff who took part said they had experienced threats, abuse or assaults over a three-year period.
Better training and risk assessment must be carried out, the report said. It added that the number of dangerous criminals probation workers deal with had more than doubled since 1983 to 14,000 in 1993.Reuse content