Former Cambridge Rindge and Latin High School classmates and co-workers of the suspected Boston Marathon bomber, Dzhokhar Tsarnaev, shared their shocked reactions Friday over their friend, acquaintance and fellow colleague's alleged attack.

Classmates called the now-19-year-old suspected bomber popular, sweet and quiet, a completely different departure from his alleged terrorist acts that caused three deaths and 176 injuries Monday and the death of an MIT security officer Thursday.

“It’s such a huge shock,” Tsarnaev’s former classmate Rebecca Mazur told Buzzfeed. “I saw the pictures last night and thought it looked kind of like him, but I felt mean even thinking that the person in the photos looked like him,” she said.

The current Harvard University student described Tsarnaev as reserved but social, stating he was known to show up at big social gatherings and was always friendly.

“He was a familiar part of the community; he didn’t isolate himself,” said Mazur, who said friends of the teen are shocked by reports that he is connected to Monday’s deadly attacks.

“I went on Facebook and so far have been reading Facebook status after Facebook status of people who are feeling shocked and betrayed,” she said.

Fellow Harvard student Junior Sam Greenberg said Tsarnaev was active in sports and friendly to him as a teen.

“We were friends. We would say hi to each other and occasionally chat. We mostly interacted on the wrestling team, and so we would just hang out after school,” said Greenberg.

An basketball buddy of Tsarnaev, who kept his identity anonymous for safety reasons, shared his reaction.

"He was literally among the sweetest, most laid-back guys I’ve ever known,” said the source. “Always friendly and welcoming. I always felt comfortable hanging out with him.”

According to a former coworker, Ryan Galuski, Tsarvnaev worked as a lifeguard at Harvard’s Blodgett Pool for two summers after he graduated high school, confirming his friendly behavior.

“He seemed very friendly, nothing that would indicate he was a weirdo or anything,” said Galuski, who said Tsarvnaev was let go after he skipped out on scheduled shifts.

PRI radio host Robin Young tweeted a photograph of Tsarvnaev Friday posing at graduation with a picture of her nephew (not named), a proclaimed best friend of the accused bomber.

My beloved nephew on right, djohar tsarnaev on left, happy cambridge Rindge and Latin grads.heartbreaking…

According to Young, her nephew claims he “never in his life” thought this would happen and is “heartbroken.”

“It’s just crazy,” another high school classmate of the suspect, Deana Beaulieu, told the AP Friday. “They always say you have to be careful with the crazy ones… That’s not something I would have ever expected from him,” she said.

Dzhokhar Tsarnaev is still at large.