Family History Progression

So I tried to find out from my dad about my Italian grandfather, but anytime I ask about his past, all I get is "I don't remember". It is very frustrating, not knowing an entire half of your history while you're actually willing to find it out. All I do know is that he is from Bari, Italy and he died when my dad was around 15/17 years old. I don't think he learned very much English, and he lived in Brooklyn, where my dad was born. Since my dad was born in 1945 I can make an educated assumption that he came "off the boat" around 5 years prior to that, maybe longer. I also know from my mom that my grandfather was much older than my dad, and my dad is the youngest of 4 siblings, two of which i did not even know existed until recently. My dad is a very secluded man and can be sort of spiteful, so these family members are pretty much on a "do not mention" understanding. I would love to know more about what my grandfather did in his lifetime, maybe one day with enough persistence I can get my dad to break down those barriers. There's just something about Italians, or even cops for that matter, and their value of secrecy and privacy. Their background makes it very hard to trust anyone with any sort of information, and this makes me sort of sad because myself and my brother lose out in the process.