By Annabal Bagdi & Joe Smith A baby-faced teen killer who was part of machete-wielding gang who slaughtered a schoolboy with an outsized machete was stabbed behind bars. Leroy Robinson was locked up in a young offenders unit while he stood trial for the murder of Joseph Riches. The stabbing incident was revealed as Robinson was sentenced for the 16-year-old’s murder. Mr Justice Wall told Coventry Crown Court that 16-year-old Robinson was at ‘risk of exploitation’ and appeared at ‘physical risk’ in detention, Birmingham Live reports. The convicted robber was stabbed while on remand during the t…