sons camera, his dad's house. legal stuff?

[mynicknamedoesntmeanathing]

If anyone knows me irl this is going to out me. So have name changed.

I bought ds1 a camera for his birthday this year. He wants to be a photographer when he's older so made sense.

He took it to his dad's house so he could take photos of his baby brother. The camera didn't come home.
Apparently his step sister moved it, even ex confirms this, and then it hasn't been seen again.

This was about 5 weeks ago. The camera has now been 'lost' for longer than he's had it.

Ex is refusing to do anything. Said it's not his problem and that ds should never have taken the camera there.

So what I want to know is is there anything I can do to make him replace/return the camera? Is there anything written in law that says he is responsible for the camera?

And as an aside how the effing Jeff can you lose a camera for so long? Surely?

Thanks

Will his dad make a claim on his contents insurance?

He said no and that it's not his fault/problem.

Sympathise totally. I have let DC take things to their dads, they never seem to come back. Then DS took things without asking. Ex refuses to return them on the grounds that 20 years ago they were his. I don't think there is anything that can be legally done but it is beyond infuriating. I am trying to send the message to DC that they have 2 equal homes and so they can choose what to have in each home. But it has to be 2-way. I am also trying to give DC values about stealing - that's working well as their dad is happy to let them steal :(

Ds1 has asked me if we can phone the police but I think they'll say they can't do anything.

That's the message I want them to have too, that they have 2 homes.
Their dad and sm don't agree though. They've told them that's not their house, ds was told he isn't allowed to take photos their anyway and that he and I are stupid for letting him take something so expensive there!

They've been bought lego before and their dad won't let them bring it home incase they lose a brick :/