In 1985, Maull was sentenced to 25 years in prison for drug smuggling. Since then, he has devoted most of his time in prison to working with dying prisoners, and to teaching Buddhist practice and meditation. In 1988, Maull helped establish the National Prison Hospice Association, which establishes hospices to help dying prisoners prepare for death. Maull is also a devout Buddhist. After establishing a meditation group in his own prison in Springfield, Missouri, he founded the Prison Dharma Network, for prisoners who want to become involved in Buddhist study and meditation.