"I think similar: it can't be Gibbs, Ziva, Vance, Ducky, Abby, Tony or Mcgee.
1. Harmon, de Pablo, Carroll and McCallum already signed contracts for season 8.
2. The show would fall apart without Gibbs as the father figur.
3. Killing Ziva would also kill the Eli David vs. NCIS storyline, which is to good to let down.
4. Vance is on promotionfotos for 7x24 so it can't be him too.
5. Ducky, Tony and McGee are on the photos for 7x23 and that looks like a crimescene for me. I suppose it's the crime scene of "the colleagues" murder.
6. As minnow226 already mentioned Abby and Ducky are in the promo for 7x23.

I think NCIS Special Agent Emil Mineoux (see Gueststar list 7x23) is the murdered colleague.
But in the promo Gibbs says to Ms. Hart: "people around me are dying" PLURAL!
And there are also lying two dead people on a beach, which is probably in Mexico.

So the much more interesting question at this moment is: Are this Mike Franks and his daughter in law or are they from a drugcartel killed by Gibbs or Mike Franks or his daughter in law.
Bell would have a motive to kill Franks and his daughter in law for revenge for his men. "

"but mike franks is not on the guest list or recurring character list for the last two episodes of this season....so maybe he will not be in the last two epssodes..................but did u hear or read anything that mike franks will be in it, but i won't be surprised if he is in the episodes cause after all it's about mexico, and anything mexioc always includes franks, right oh wll...............but if franks is not in the epsiode, then i would be surprised."

"

I think NCIS Special Agent Emil Mineoux (see Gueststar list 7x23) is the murdered colleague.
But in the promo Gibbs says to Ms. Hart: "people around me are dying" PLURAL!
And there are also lying two dead people on a beach, which is probably in Mexico.

"

"7x23 "When a colleague's murder sends shockwaves through the team, Gibbs uncovers a surprising link to the crime. (CBS Synopsis)"

The press release says that this murder will send shockwaves through the team.
"devastating" was mentioned with the decision Gibbs has to make and I think that can mean quiet a lot like: turning himself over to mexican authorities, running from the trial for murder, killing someone who doesn't deserve it, ...

And when I remember there was an NCIS Agent killed in season one or two, that was shocking for the whole team even if they didn't know him very well. (I think that was the episode were Tony kissed the transsexual woman.)"

"7x23 "When a colleague's murder sends shockwaves through the team, Gibbs uncovers a surprising link to the crime. (CBS Synopsis)"

The press release says that this murder will send shockwaves through the team.
"devastating" was mentioned with the decision Gibbs has to make and I think that can mean quiet a lot like: turning himself over to mexican authorities, running from the trial for murder, killing someone who doesn't deserve it, ...

And when I remember there was an NCIS Agent killed in season one or two, that was shocking for the whole team even if they didn't know him very well. (I think that was the episode were Tony kissed the transsexual woman.)"

"That agent's death could be just the tip of the iceberg..."