I found something interesting...while we can disprove it was the 8th potentially at the Graduation Massacre, we can still assume it was an Apostle and that's why Zack showed up there.
a few years ago, which means there's a chance that one of the corpses were recovered at the Massacre?
A
couple more of them leads me to believe 2, as is later solidified by saying
BOTH were corpses. We know of those recent 2 one was the 8th and the other is probably the one Claudia is getting of similar properties. Perhaps she's getting Life? As we know Light can heal people in the Battle of Diamonds, Claudia has a kind hearted nature about her, perhaps a monster that spreads non violence is just what would suit her, allowing her to still help Tiffany.
My guess is the 1st one recovered years ago was the one at the Massacre, and also the one that injured Zack and his squad. If true, perhaps it was in correlation to the 7th in some way and Ella was warned about it through the 4th? Who knows.
If I was a monster that despised a certain Apostle pair, and I knew I couldn't physically hurt them, but COULD hurt their spawn that potentially carries out their motives; it would make sense to go hunt them down while they are weak, especially when it was fresh news. Even Valravn could detect when the 2nd made it's move, or Aglaecwif hearing about the 1st taking on a spawn despite it's rarity. There's a good chance:
-Sometime in that Ella year obtaining her powers, she got her powers from the 3rd & 4th Avatars.
-Their descent attracted the 7th (i.e recognizing it in the Dead End and saying it's not possible). Maybe she was shocked how it descended again so fast after being defeated?
-The 3rd & 4th held it off, we know they have intervened against the 1st, why not team up against the 7th?
-Ella retreated home and lost both her parents to it. But it ended up being defeated by the 2 of them together (3rd & 4th)?
-She kept running, did some soul searching as an orphan and discovering her newfound powers, where she met a young boy named MC, that she grew close to for a brief time.
-The 3rd & 4th let her in on their plans to combat the crazy ass force that is the 7th and his possy, and that's to get the Arbiter, but they'll need a vessel for themselves and it.
-At first she wants nothing to do with it, explaining her outbursts talking to herself when she gets back with Christie.
-The 7th is furious to be beaten by his leaders, so he sends one of his loyal followers (9th, 10th or 11th?) To go kill the 3rd & 4th, assuming they are still close to the spawn.
-Turns out the 3rd & 4th were a wee bit too drained from that encounter with the 7th, and instead warn Ella that one of the Apostles is nearby, and after her.
-This would explain why Ella only stops Christie AFTER the fact that they are already there at the party site, she knocks Christie out and is about to run.
-Whatever Apostle was sent, doesn't know what Ella looks like obviously, but knows they are nearby and are a kid to boot, narrowing down it's targets to only the grade rather than the faculty onlookers. We know the Dark followers aren't exactly the most caring bunch, so it starts slashing down the students.
-Considering it is an Apostle, it happens in a matter of seconds, before Zack arrives a little late to the party and takes the thing on alone with his squad.
-Ella watches from the side lines explaining why she was still there at the Massacre, yet not a suspect on H.E.R.O's radar FOR the murders, instead listed as a survivor.
-It also explains the tall man wearing a hood from one of the eye witnesses. For him to claim HE was responsible, either he got in late to see only him standing atop the bodies or it all happened INCREDIBLY fast and Zack pushed himself a little TOO far to end it quickly, explaining why it's taken YEARS even WITH an Evolution later on to recover.
Bam! Bit if a stretch I know, but I feel like this Massacre is gonna tie in a lot of shit later on.