A third degree crime is punishable by up to 5 years in New Jersey State Prison. Someone with no criminal history is potentially eligible for PTI which is a diversionary program designed to keep someone out of jail/prison. When someone completes PTI, their record shows no evidence of a conviction. If the prosecutor does not want him in PTI he might get probation. Sometimes people get straight probation, sometimes the probation is conditioned upon time in the county jail. There are also sentencing concerns for someone who is a repeat offender (potential for extended term beyond the 5 years - up to 10 years), but it is highly unlikely that an 18 year old would qualify.
Have him consult an attorney who practices in his area for advice on how to proceed because there are thousands of options that could play out in his case.
Best of luck to him - Jeff Barile
DISCLAIMER This answer is provided solely for informational/educational purposes. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising.
In answering your question, I assumed you meant burglary as listed in the content of the question. There is no 3rd degree robbery as mentioned in the title. It's common for people to substitute those two words. -Jeff B.
