1,566 prisoner deaths from 1993 to 2002. A preliminary report suggested that nearly one third of the cases involved suspicious circumstances. However, in June, the Ministry announced that there was evidence of abuse only in the two Nagoya fatalities. Regarding the other suspicious deaths, the Ministry said that approximately 10 deaths could be attributed to poor medical care. The authorities reported they had lost the documentation on nine deaths in Tokyo's Fuchū Prison. The remaining deaths were determined to be "not suspicious". As of May 2019, Japan has not signed nor ratified the Optional Protocol to the Convention against Torture and other Cruel, Inhuman or Degrading Treatment or Punishment. Prison system Prison conditions met international standards; although some lacked adequate medical care and sufficient heating in the winter or cooling in the summer and some facilities were overcrowded. Prisoners were not allowed to purchase or receive supplementary food. While death records are kept for 10 years, many of them were missing, which sparked an ongoing review of the prison system. Prisons operated at an average 117% capacity. In some institutions, two inmates were placed in cells designed for one inmate, and thirty or sixty in cells meant for 15. According to prison officials at Fuchū and Yokohama prisons, medical attention was inadequate. The MOJ's Corrections Bureau likewise acknowledged that correctional facilities lacked medical preparedness. The Government's Project Team on Medical Issues of Correctional Institutions continued to consult with related organizations on such issues as increasing medical staff, upgrading medical conditions during nights and weekends, and strengthening cooperative relationships with medical institutions in the community. In May, the Minister formed a subcommittee to improve prison medical facilities. In some institutions clothing and blankets were insufficient to protect inmates against cold weather. Most prisons did not provide heating during nighttime hours in winter despite freezing temperatures, subjecting inmates to a range of preventable cold injuries. Foreign prisoners in the Tokyo area continued to present to visiting diplomats during the year fingers and toes affected by chillblains of varying severity, the direct result of long-term exposure to cold. According to the Japan Federation of Bar Associations, the authorities are permitted to read letters sent or received by prisoners and they are not required to disclose this practice to prisoners. If the content is deemed "inappropriate", the letter may be censored or confiscated. All visits with convicted prisoners were monitored; however, prisoners whose cases