Fire fish died today...red marks... could starfish kill it?

[RedSea50Gang]

I just bought a fire fish Sunday from my lfs. I also got a sand sifting sea star the same day. My tank is a mix of corals and fish... I also have a fire shrimp. Today is Wednesday and he did hide a lot in a cave since I got him, but when he came out he was swimming around fine and coming out and aggressively eating the frozen mysis I put in the tank to feed... he died while I was at work and my husband tells me it almost looked like the starfish was trying to eat him... he pulled him out and put it in a bag of water. I noticed on one side he had some light reddish marks and I don’t know if it’s disease or something attacked him. He looked fine otherwise and I tested my salinity and did a water change after and will take my water to get tested tomorrow to make sure all is alright... could the starfish have killed it??? I read starfish can sneak up on sleeping fish... but I am not sure... the starfish also climed up to the top of the tank today fell then buried itself so I don’t know if it’s starving but I have plenty of pods in the sand bed... probs a whole other thread but should I supplement feed the starfish?? photos of pre death and post death included of

 

[Jekyl]

Star fish wasn't the killer. Just the janitor.

 

[RedSea50Gang]

Star fish wasn't the killer. Just the janitor.

I wish my husband left it in there for him to eat I don’t know what to supplement my sand sifting starfish’s diet with... or if he’s good on copepods... I have them all in my sand and live rock... I hear detritus was a lie. I tried to squirt frozen mysis near him and towards the sand around him but no clue how or if he’d get that!