More breaking details in the Petraeus scandal

>>> welcome back. today we learned another general has been caught up in the investigation that led to the resignation of cia director david petraeus . general john allen is the top u.s. commander in afghanistan . officials are investigating him for, quote, inappropriate communication with jill kel kelley . she's the woman that got the petraeus investigation started. the pentagon is looking at more than 20,000 pages of documents and e-mails between kelley and general allen . 20,000. officials tell the ap that some of the material was, quote, flirtatious. general allen denies having an affair with kelley , who we know was also friends with general petraeus . joining me now is michael isikoff , national investigative correspondent for nbc news. he's been breaking some of the big details on this case over the last few days. michael, first, thanks for being here tonight.

>> thank you. good to be with you.

>> now, let me ask, general allen is now under investigation for his relationship with jill kelley . what can you tell us about the relationship and what can you tell us about miss kelley .

>> we should say we don't know for sure. as you pointed out, the e-mails, these voluminous -- apparently voluminous e-mails describe a relationship or -- that appear to be flirtatious but, you know, potentially inappropriate is the word that was first used by the pentagon. but whether it goes more than that, we don't know. we do know that at least one woman, paula broadwell, appeared to believe there was something there because she's the one that started out these anonymous threatening e-mails which i should remind you, start out not referencing jill kelley 's relationship with general petraeus with other generals at u.s. central command and special operations command in tampa. now, we should remember that general allen , before being the commander of all u.s. troops and nato troops in afghanistan was the deputy commander at the u.s. central command . so, the presumption would be that it was kelley 's relationship with general allen , whatever that was, that set paula broadwell off and led her to begin these anonymous e-mails.

>> what was it, 20,000 pages of e-mails? i mean, what kind of issue could it have been, then?

>> you know, the 20,000 could be a little misleading. that's 20,000 doumencuments in total printed out. there may have been extensive attachments to these e-mails that could have been hundreds of pages. until we see them, you know, it's hard to make a firm judgment. we're expecting a statement from jill kelley 's lawyers and communications advisers this evening in which she, i can presume, is directly going to address this. she's already denied there was any inappropriate relationship with general petraeus . so, i don't want to be too hasty in rushing for judgment, but we should point out that there are some very odd things going on here beyond the voluminous e-mail correspondence. we learned about general petraeus and general allen writing letters in a -- to a d.c. judge on behalf of jill kelley 's sister, who's involved in a very nasty child custody case. this was just two months ago. september --

>> so just two months ago --

>> just two months ago, while the fbi investigation was going on, both general petraeus and cia director and general allen and as commander of u.s. forces in afghanistan , within two days of each other, write letters vouching for the sister of jill kelley saying she deserves more time with her son. a judge had placed very strict limits on her visitation with her own son after awarding custody to her ex-husband. the judge had found -- the judge had found, and i quote, that jill kelley 's sister has extreme personal deficits in the areas of honesty and integrity. that was in a court ruling in november of 2011 . and then in september of 2012 the director of the cia is writing a letter vouching for --

>> so, the judge has this assessment of jill 's --

>> jill kelley 's sister.

>> right, right.

>> and then general petraeus , as districter of the cia and general allen both wrote letters this past september on behalf of this sister as a favor to jill kelley ?

>> well, we can presume as a favor to jill kelley , general petraeus , then- cia director petraeus referenced spending time with the sister and her son, young son, while the kelley family, including jill kelley , was visiting with him over christmas, at a christmas dinner at the petraeus home. so, clearly there was a very close relationship there between the kelleys and the petraeuses.

>> how does this woman, jill kelley , get to close to all these generals?

>> well, you know, that is one of the big unanswered questions here. she clearly had a lot of access to a lot of high-level people in the tampa area. she lived within a mile of central command and special operations command are located. she made a point of volunteering for events and being very social and friendly with a lot of high-level people in the government, high-level generals in that area.

>> michael isikoff , we'll be following this, of course, with your help. thanks for your time tonight.

>> thank you.