Non US-Citizen investors?

Hello

A good friend of mine who lives in Mexico would like to invest in the US stock market, preferably via US Mutual Funds or ETF's.

He is not a US Citizen. He can travel to USA (he has immigration papers for this) and open up a US bank account if need be.

Is this possible? What does he need to do?

Thanks

hi, im a non us citizen and i would like to know, what i need to do so i can start investing in the us stock market, ty