People said (that) her husband was a criminal.

这个句子中said后接宾语从句。这个句子改为被动语态时，有二种该法：

1 It was said that her husband was a criminal.

that从句由宾语从句改为主语从句，it作形式主语，that从句外置。was said的主语是个that从句。

2 Her husband was said to be a criminal.

用宾语从句的主语作被动句的主语，said 改为被动语态was said. 宾语从句的谓语动词was a criminal 改为不定式to be a criminal, 作被动句的主语补足语。

语法上Her husband是was said的主语，但语义上was said的主语是“她丈夫是个罪犯”这个判断句。这种结构语法上称为“提升主语结构”（raised subject）。即从句的主语提升到主句作主句的主语，从句的谓语改为不定式结构作主语补足语。至于不定式用to do还是to have done, 取决于从句谓语和主句谓语的时间关系。如果二者是同一个时间，则不定式用一般体。如果从句谓语时间在主句谓语时间之前，则不定式用完成体。

所以：

People said that there was gold in the cave.

改为提升主语结构则为：

There was said to be gold in the cave.

如果主动句的谓语为现在时，宾语从句为过去时，改为提升主语结构时，不定式要用完成体：

 People say that there was gold in the cave.

There is said to have been gold in the cave.

再看一个提升主语结构：

It seems that Tom left yesterday.

Tom seems to have left yesterday. (提升主语结构）