在英语中，in possession of 和 in the possession of 都可以说，但意思不同：前者表示“拥有（持有、占有等）……”，后者表示“被……拥有（持有、占有等）”。如：

The brothers were caught in possession of stolen property. 兄弟俩因非法拥有被盗物品而被捕。

The city was still in the possession of the British troops. 这座城市还处于英军占领之下。

Those documents are now in the possession of the Guardian. 那些文件目前在《卫报》手里。

你的句子：

He was found in possession of explosives. 他被发现私藏爆炸物。

比较同义表达：

这房子是吴先生的。

正：Mr Wu was in possession of the house.

正：The house was in the possession of Mr Wu.