Taxation on a u.s citizen in u.s.a on the indian incomes

Hi Friends,

I Would like to know the tax implication of the following case in case of a US Citizen over incomes earned in India.

Mr X was born 30 yrs back in USA, and returned to India when he was 10 years old, with his parents and permanently settled in India. But he is continuing USA Ctizenship and USA Passport due to birth in USA.

Mr X is Earning Business and interest from his operations in India. Mr X has no home or connection in USA since last 20 years.

My Question is he is already paying taxes in India on his Above Income, But is he Liable to Tax on these incomes in USA.

If anyone can help me on this please help me.

Thanks