Mr Williams was convicted of 15 offences of damaging property being reckless as to whether life was endangered, one of assault causing actual bodily harm and one of common assault.
Mr Williams threw rocks at people whilst in his delivery van. The case has been adjourned for a psychiatric report.
Judge Martin Joy warned he was considering a jail term of at least 10 years:
"These were frightening and very shocking offences, all of them very serious and going to require a deterrent sentence," he said.
"The impact on many victims has been very considerable and it is likely the prison sentence will be in terms of double figures."
Mr Williams was remanded in custody until his sentencing hearing, which is expected to take place in about six weeks time.
Alex Rooke maintains a busy 50/50 defence and prosecution practice, and believes this is the best way of learning and retaining the skills applicable to both sides of the courtroom. He has wide experience of cases involving serious violence, grave sexual offending, fraud and organised crime.