Mr Sunny Swee still remembers the first two of his three stints in prison.
"It felt like a holiday. I didn't think much of it, but it made you more convincing as a gangster - as if you had more credibility," said Mr Swee, who served about three months for his first sentence when he was 18, and about seven months in his second stint in jail at age 23.
Then, he indulged in an assortment of vices, including illegal gambling, selling pirated VCDs and drug abuse.
Now, his criminal past is a faraway memory and he has embarked on a journey that he never thought possible when growing up.
The 33-year-old started school recently at the Nanyang Technological University's physical and mathematical sciences school, alongside students a good 10 years younger than him.
He is juggling eight modules - two more than the average undergraduate. This includes two higher-level calculus and linear algebra subjects that require applicants to take a qualifying test first.
Mr Swee said he had always been good in mathematics in school, but studying was never a priority.
At 14, he needed pocket money, so he started working at fast-food chain KFC. When work took up too much of his time, he skipped school.
At 17, he started betting on football matches illegally. When his gambling debts mounted, he turned to selling drugs and pirated VCDs, making $10,000 a month.
After two prison stints, he found himself behind bars a third time after he was caught by Central Narcotics Bureau officers in a drug bust in Ubi in 2009. He served close to six years and was released in February.
It was only during his third spell in jail that he settled down to study.
"There was so much time in prison and nothing to do. It was the first time I thought hard about my life, and felt worried about my future," he said. "I hadn't done anything apart from helping my mother occasionally."
His mother runs a noodle stall at a coffee shop in Bukit Batok.
His parents are divorced and he does not see his father much.
He has three siblings - two sisters and one brother - who all stopped studying after completing secondary school.
Less than two years into his third jail stint, he enrolled in prison school where he did his O- and A-level exams.
The Straits Times first spoke to him in March last year in the Tanah Merah Prison School after he emerged as the top A-level scorer among 20 candidates in the prison school, scoring As in mathematics, principles of accounting and mother tongue, B in business management and economics, and D for General Paper.
"When I was in prison school, my teacher asked me about my plans after completing my A-level exams. It was then that I realised education has given me a way out of crime," said Mr Swee. "If I didn't study, there is a high chance I will go back to my old ways."
His older sister, 34-year-old Honey Swee, said she was immensely proud of her brother for making it to university.
"I always knew that he could study if he put in some effort. I guess he was just very distracted in his younger days," she said.
The siblings were born on the same day, a year apart. "Because of this, I always feel a special connection with him. He was rebellious growing up and we had our fair share of fights, but he would never raise his voice at me."
She added: "It upset me a lot to see him on the other side when I visited him in prison. But maybe it is something he has to go through in life to learn."
These days, Mr Swee's schedule is packed. Apart from school, he tutors part-time and attends church on weekends.
He still helps his mother at the noodle stall sometimes, and volunteers at self-help group Beacon of Life, which provides support to former inmates.
Based in Taman Jurong, the group was set up by artist Kim Whye Kee, 35, and lawyer Darren Tan, 36, both former inmates.
Mr Swee was introduced to the group by an old friend, 32-year-old Kenji Joo, who also served time for drug-related offences.
The group also mentors at-risk teenage boys. They help them with their school work and organise excursions to places such as Pulau Ubin.
Mr Swee said: "I enjoy mentoring the youngsters. It gives me a sense of satisfaction. I see a bit of my younger self in the boys - lost and without guidance.
"I want to help them and make a difference in their lives."