FORGET ALL THE SMART ANSWERS.
The USA doe's share information with the Police in the UK and of course every piece of info held on the PNC or the Police National Computer.
Your UK criminal record and DNA is held for the duration of your life.
The USA through the super computer run by the NSA or the National Security Agency can and will check in seconds.
THINK ABOUT THIS : Say your friend was convicted of terrorism or plane hijacking or murder, and served his time 12 yrs ago, are you telling me that ticking a simple box on a visa form will allow him access to the USA ?.
Would you want to share a plane with a terrorist or a hijacker ?.
DOH ! - No not me either !
Want some advice - RING THE USA EMBASSY IN LONDON, and get it from the horses mouth.