Assistant Attorney General

A lighning rod is placed on the roof of a house to attract lightning instead of the lighning charging the house.
In this case lighning rod mean the memo attracts controvesy.

On record means "publicly" and/or officially, usually this means his position is recorded in writen form. in this case the legal memo is the written form. sometimes on record can mean being quoted in the press either television or newspapers.
Counsel Jay Bybee, was one of the first and most senior government officials to publicly and officially consider controversial interrogation tactics permissible.

A legal memo is very different from a business memo (short for memorandum), which is often just a note between two business people. A legal memo often contains legal research and can sometimes be used as the foundational information for drafting legal briefs, motions, complaints or answers, all of which are used when a case is litigated. To complicate matters, lawyers or law clerks or paralegals can write legal memoranda even after a case has begun to be litigated, but there can be no complaint, answer, motion, bill of particulars or brief until the case is actually in litigation (e. g. a lawsuit has been filed).

A memo is a note usually when you want to tell someone something but it does not need a fully formatted letter.

still not feeling well . Here are those places which is stopping me..

later become a lightning rod for controversy ----> lighting rod ==attacting controversy . I understand , lighting rod's are used is house to lit the house.....but in this context is it just analogy to mean 'attracting controversy' ?

'went on record'---->officially appointed

'controversial interrogation tactics permissible' ---->permissible ? are they trying to say interrogation tactics to be made public . .....was it a forbidden earlier and now it has to be permissible ....is it something like this ?

' Geneva Conventions irrelevant in dealing with so-called unlawful enemy combatants.'---->is that law too weak to deal with terrorist ?

I'm not sure which direction this text moves ...I may not aware of international laws or Geneva Conventions deals ......so if anybody can throw some light in this context that'll be just wonderful.

Nice to learn some new facts ....thanks for your valuable time.

No, not appointed. I used the word position which has confused you.

on record = it is officially recorded (in the memo) that this is my opinion.

'controversial interrogation tactics permissible' ---->permissible ? are they trying to say interrogation tactics to be made public NO not public . .....was it a forbidden earlier and now it has to be permissible YES

The Geneva Conventions are made up of four treaties and three additional protocols that set the standards in international law for humanitarian treatment of the victims of war.
The language is extensive, with articles defining the basic rights of those captured during a military conflict, establishing protections for the wounded, and addressing protections for civilians in and around a war zone. The treaties of 1949 have been ratified, in whole or with reservations, by 194 countries.[1]
source.
http://en.wikipedia.org/wiki/Geneva_Conventions

are you able to access the linked material?

Geneva Conventions irrelevant in dealing with so-called unlawful enemy combatants.

Because countries dealing with terrorists are not at war in the accepted sense (one government says we declare war on your country to anothe government) the terrorist is considered an unlawful combatant and not subject to the geneva convention.

beautiful ...so much of information !.... I'm glad to know all these things ...thanks for your time