I don't think we can find out who the other merged one was D4. The evidence for a merge is solid, but only because of one report. But there's 4 (maybe 5) possible other targets. One of them shouldn't have a private chat, but with 4 or 5 possible hits, that probably doesn't rule down enough to get useful.
Probable known targets for merging with Esteemed BlackHeartKabal N3, presuming the target has to not have a private chat:
1) Not Esteemed Knightwing64, who died town and sure doesn't seem to have had a private chat, but who was clearly targeted for vote steal.
2) Not Esteemed notquitethere, who died town and targeted by Esteemed Imp, and I didn't get a report of two sets of results.
3) Not Esteemed Jim Groovester, who claims a private chat.
4) Not Esteemed Elephant Parade, who claims a private chat.
5) Not Esteemed ToonyMan, unconfirmed alignment and reported to lack a private chat - however targeted by Esteemed notquitethere, who reported confusing results for what appears to have been the photograph ability, but didn't report two sets of them, including Esteemed Lenglon (I would expect that if merged here).
6) Not Esteemed Maximum Spin, unconfirmed alignment but targeted by Esteemed hector13 for a status gain.
7) Almost Certainly Not Esteemed Imp, I'm still not in a private chat, but Esteemed ToonyMan said only targeted me. However, could it be possible Esteemed ToonyMan's ability doesn't report if hitting two targets, I have no idea.
8 ) Possibly Esteemed Hector13, confirmed town, probably without a private chat, and with no known targeters N3.
9) Possibly Lenglon, unconfirmed alignment or private chat status but no known targeters N3 (since Esteemed BlackHeartKabal is ruled out).
10) Possibly Esteemed The Canadian kitten, unconfirmed alignment but no known targeters N3.
11) Possibly Esteemed Secretdorf, unconfirmed alignment but no known targeters N3.