Yes, they were the two catalytic converters. Scrap value around £350-400 so not a bad five minute's work. M54's have two sets, the small manifold ones (manicats) and the main ones. Only BMW make/sell the main ones.
That's a job for your insurance company - chances are they will write the car off but it'll be a £1500-£2000 repair.
Otherwise you'll need to find an exhaust specialist who can weld a pair of aftermarket cats in. They are worthless for scrap.
You just cannot park a petrol car outside overnight any more with such low hanging fruit.