The death of serial killer Harold Shipman at Wakefield Prison in January 2004 "could not have been predicted or prevented", a report has found.
Shipman hung himself using a ligature made from bed sheets
But Prisons and Probation Ombudsman Stephen Shaw said the death raised "procedural issues relating to the management of the incident".
His report examined how the former GP was able to kill himself in his cell.
Mr Shaw criticised decisions which had curbed Shipman's prison privileges, meaning he could not ring his wife.
The former Hyde GP used a ligature made of bed sheets to hang himself from his cell window.
The serial killer had served just four years after being given 15 life sentences for murdering 15 patients. However, he is thought to have killed a further 235 patients.
Mr Shaw said procedures dealing with at-risk prisoners such as Shipman needed to be re-examined.
Shipman had been on suicide watch when he came to the prison, but was subsequently taken off it, an inquest heard in April.
Mr Shaw dismissed allegations that Shipman had been taunted into killing himself by prison officers.
But he said staff should have been given more information about his state of mind.
He said: "I am critical of the fact that staff at Wakefield do not appear to have been alerted to the man's long-term risk of suicide or what might finally trigger it."
Shipman's privileges had been dropped from standard to basic because he had refused to take part in courses in which inmates are encouraged to discuss their crimes and admit their guilt.
This meant he could no longer afford to ring his wife Primrose and he was described as "very emotional" and "close to tears" by prison doctor Sunil Spirvastava weeks before his death.
Mr Shaw's report made 17 recommendations and was critical of Wakefield's record-keeping, which meant the exact timings of events leading to Shipman's death could not be established.
The report found prison staff tried to resuscitate Shipman for around half an hour, but Mr Shaw said he was "critical" of the failure to call paramedics and the delay in calling a doctor.
The doctor arrived two hours after the body was discovered, but Mr Shaw added he had "no reason to believe" he could have got there faster as he lived on the other side of Leeds.
Shipman died a day before his 58th birthday, meaning his wife was given his full NHS pension as he was under 60.
Peter Atherton, director of High Security Prisons, said the service was pleased the report found the death could not have been prevented.
"The report has been with the Prison Service for some time, during which we have drawn up an action plan," he said.
"The report makes 17 recommendations, every one of which we have accepted and have either implemented or are in the process of doing so."
However, some of the friends and families of Shipman's victims say they feel cheated by his death and have been critical of the Prison Service and the report.
Gloria Ellis, who found her close friend Winifred Mellor, 73, dead after one of Shipman's home visits in 1998, said prison authorities should have "kept a closer eye on him".
"They left him unattended when he should have been watched. Now I just want to put a line under it all," she said.
Angela Wagstaff, whose mother-in-law Kathleen Wagstaff, 81, was murdered by Shipman at her home in 1999, said her feelings were mixed.
"In some ways I'm glad because it means all this will stop keep coming up, over and over again, but also maybe I feel he did not serve long enough," she said.
"The theory was it was all about control with him and he was still in control. He called the shots and decided what was going to happen to him."