43,622 in 2005 to 15,276 in 2016. Most common offenses committed by foreigners were theft (60% of their Penal Code offenses), immigration violations (66% of non-Penal code offenses), and drug offenses in 2016. The number of convicted foreign prisoners was 3,509 in 2016. Yet, most of them were given suspended sentences and only 744 were imprisoned in the same year. The largest group was thieves (122 people) and the second largest was drug offenders (96 people). Use of volunteers Volunteers are also used in supervising parolees, although professional probation officers generally supervise offenders considered to have a high risk of recidivism. Volunteers hail from all walks of life and handle no more than five cases at one time. They are responsible for overseeing the offenders' conduct to prevent the occurrence of further offenses. Volunteer probation officers also offer guidance and assistance to the ex-convict in assuming a law-abiding place in the community. Although volunteers are sometimes criticized for being too old compared with their charges (more than 70 percent are retired and are age fifty-five or over) and thus unable to understand the problems their charges faced, most authorities believe that the volunteers are critically important in the nation's criminal justice system. Claims of inmate rights abuses Amnesty International has cited Japan for abuse of inmates by guards for infractions of prison rules. This abuse is in the form of beatings, solitary confinement, overcrowding, or "minor solitary confinement" (keiheikin), which forces inmates to be interned in tiny cells kneeling or crossed legged, and restrained with handcuffs for prolonged periods of time. In 2003, Justice Ministry formed a special team to investigate 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 Fuchu Prison. The remaining deaths were determined to be "not suspicious." In the wake of prison abuses, the "Law Concerning Penal Institutions and the Treatment of Sentenced Inmates" came into effect on June 7, 2007, to reform treatment on prisoners, such as "the expansion of prisoners' contacts with the outside world, the establishment of independent committees to inspect prisons,