It doesn’t say the paper was the entity engaged in the raid. If I didn’t know the broader context, I would assume that sentence meant “A newspaper was investigating a police chief at the time the police chief’s home was raided by another law enforcement agency”. That seems way more likely than a newspaper being referred to as “him”.
There is only one person mentioned and therefor "his" can only refer to that person. "His" can not refer to the newspaper.
[0] "Paper investigating police chief prior to the raids on his office and home."