Prior to the sentencing, Cobb had been placed on probation five times.
Cobb's mother said she blames the juvenile justice system for letting her son off easy, for previous offenses.
"I have peace of mind knowing that you will not be on the streets anymore. I did not deserve this, the other victims did not deserve this and your family does not deserve this either. You deserve to be in prison," said one of Cobb's victims.
Victim after victim stood up in court, saying how relieved they are Cobb isn't able to terrorize the community anymore.
Richard Fazi lived across from Cobb.
Despite Fazi treating Cobb like family, Cobb broke into his home and stole a gun.
"I took him in as a son and to hear all this from these people, what he did and to myself, well, you did it, now you pay the consequences. We'll all survive. What about you?" Fazi said.
Cobb pled guilty for six separate violent attacks and armed robberies from March through June of 2017.
One of his recent crimes was explained in graphic detail.
"Cobb then grabbed (the victim's) purse, they struggled. Mr. Cobb then pushed her to the ground and smashed her head into the ground, and punched her in the face," explained John Hirshauer from the Cuyahoga County Prosecutor's Office.
"These were not spontaneous acts. They were cold and calculated," said a Cleveland State University Police Officer.
Cleveland State police explain surveillance video shows Cobb stalking his victims before the attacks.
"We have images of him hiding behind cars like he was approaching prey," the officer said.
Cobb's first arrest was in 2012. His mother was not in court Tuesday, but wrote a letter saying she begged juvenile court judges to give her son harsher penalties.
"I have personally called Judge Rini's courtroom and talked to her and ended up leaving messages with her bailiff on numerous occasions, begging and pleading for more help and to be stricter on Montez, but with no avail," she wrote.
With that, judge Nancy Russo sentenced Cobb to 30 years behind bars.
"What you have done here has traumatized so many families, including your own," Russo said.