Squirrel watching

Leo didn’t think much of being confined to barracks last night after he brought in a red squirrel.
This morning, I asked M for his whereabouts because I could not see him in his usual spot tucking into his breakfast in the kitchen.
M shrugged. “No idea”.
A quick check of the cat flap revealed he had absconded in the night despite the heavy bag I placed against it. He had managed to move it enough to squeeze through.
What to do? 
PS. He's already gone out for the night before I had time to stop him.