How was he able to commit this and apparently several other attacks if he was monitored?
Here is a good article explaining this.
"The monitors are mainly used to ensure that parolees report to their parole officers and don't leave the area. They also can be used after the fact to see if parolees were near areas where crimes occurred. Those on GPS monitors aren't watched in real time. Authorities use software that allows them to punch in the parameters of where the parolee is allowed to go or not go. But even if the parolee violates those conditions, authorities often aren't notified immediately."