How can I investigate if my father is gambling?

Tagged weird as some can wonder why do I need to do it.

Since I was a kid, my mother always complained that my father is not good with personal finances. Weird that he didn't have huge savings. I was affected by it when my dad borrowed me some money from me for a new car that we'll buy to my mom and some amount to lend his friend.

After we got the car my mom complained about my dad borrowed some money from my mom with the same purpose he got from me. I don't think he will pay back to both of us.

Considering past year experiences I have serious concerns that my father could be gambling. I fear that he could be betting on football games. I've caught him couple of times and he used to hide the phone when I asked him how you doing.

At this stage I don't think I can point this question directly to him.