They are charged with the crime of deliberately feeding their baby son the heroin substitute, methadone, month after month until he died. Mark Bate and Gemma Fennelly from Hartlepool - both heroin addicts - appeared in court today accused of manslaughter. Their 22-month-old son, Mitchell, died in September 2005. Doctors found significant amounts of methadone in his system. There was also evidence of cocaine and heroin in his body.