keisatu ga sono hito no syoutai wo sirabeta.

It is read:

けいさつ が その ひと の しょうたい を しらべた。

Word by word:

• 警察 = けいさつ
• その = その
• 人 = ひと
• 正体 = しょうたい
• 調べた = しらべた

警察 usually means the police in a general sense, not necessarily one specific officer.

In Japanese, 警察 can refer to:

• the police as an institution
• the police in general
• sometimes police officers collectively, depending on context

So in this sentence, it most naturally means the police investigated that person’s identity.

If you specifically wanted to say a police officer, you would more often use 警察官.

が marks the grammatical subject of the sentence: the one doing the action.

So:

• 警察が = the police is the one who investigated

In this sentence, が simply identifies 警察 as the subject.

A learner may wonder why it is not は. Both can sometimes be possible, but the nuance changes:

• 警察がその人の正体を調べた。 = focuses on who did it or presents it as a straightforward event
• 警察はその人の正体を調べた。 = topic-focus, more like as for the police, they investigated that person’s identity

So が is very natural here.

その means that and modifies the noun that follows it.

So:

• その人 = that person

Japanese has a three-way distinction:

• この = this ... near the speaker
• その = that ... near the listener, or already mentioned
• あの = that ... over there / distant from both

In many cases, その is used for something already known from context, so その人 often means that person we’re talking about.

の connects nouns and often works like of or shows possession/association.

So:

• その人の正体 = that person’s identity
• literally, the identity of that person

Here, の shows that the identity belongs to or is associated with that person.

This is a very common pattern in Japanese:

• 私の名前 = my name
• 日本の文化 = Japan’s culture / the culture of Japan
• 彼の車 = his car

正体 means true identity, real nature, or who someone really is.

In many contexts, it has a slightly dramatic nuance, like:

• someone’s real identity was unknown
• someone was hiding who they really were
• people were trying to find out what someone really was

So その人の正体を調べた is stronger than just checked their name. It suggests investigating who that person really is.

Depending on context, translations could include:

• investigated that person’s identity
• looked into who that person really was
• investigated that person’s true identity

を marks the direct object of the verb.

Here, the verb is 調べた = investigated / examined / looked into, and the thing being investigated is その人の正体.

So:

• その人の正体を = that person’s identity as the object
• 調べた = investigated

Together:

• 警察がその人の正体を調べた。
• The police investigated that person’s identity.

The dictionary form is 調べる.

調べる means:

• to investigate
• to examine
• to look into
• to check

調べた is the plain past form, so it means:

• investigated
• looked into
• checked

This is an ichidan verb:

• dictionary form: 調べる
• past plain form: 調べた
• polite form: 調べます
• polite past form: 調べました

Japanese is basically an SOV language:

• Subject
• Object
• Verb

So the normal order is:

• 警察が = subject
• その人の正体を = object
• 調べた = verb

That is why the verb comes at the end.

English usually uses SVO:

• The police investigated that person’s identity.

Japanese typically saves the main verb until the end of the sentence.

It can change more than in English because the particles show each word’s role.

For example, these can still be understood:

• 警察がその人の正体を調べた。
• その人の正体を警察が調べた。

Both mean basically the same thing, because:

• が still marks the subject
• を still marks the object

However, word order changes the emphasis and what sounds most natural in context. The original order is very standard and neutral.

Japanese does not normally use articles like the and a.

So nouns like 警察, 人, and 正体 do not need separate article words.

Whether something is understood as:

• a
• the
• or sometimes no article at all

depends on context.

For example:

• その人 already means that person, so it is specific
• 警察 in context is understood as the police

Japanese relies much more on context than English does.

This sentence is in the plain style because it ends with 調べた.

Plain style is commonly used in:

• casual conversation
• written narration
• news-like summaries
• dictionary-style examples

A polite version would be:

警察がその人の正体を調べました。

Here:

• 調べた = plain past
• 調べました = polite past

Both mean the same thing, but the level of politeness is different.

Yes, it can.

Because 正体 often means someone’s true identity or real nature, the phrase can suggest:

• the person was suspicious
• the person may have been hiding something
• people did not know who the person really was

So this can sound stronger or more dramatic than a simple phrase like:

• その人について調べた = investigated that person
• その人の身元を調べた = checked that person’s identity/background

正体 often gives a feeling of uncovering something hidden.

Yes, but the meaning changes slightly.

• 警察 = the police
• 警官 = police officer
• 警察官 = police officer, a bit more formal/explicit

Compare:

• 警察がその人の正体を調べた。 = The police investigated that person’s identity.
• 警察官がその人の正体を調べた。 = A police officer / police officers investigated that person’s identity.

So 警察 sounds broader and more institutional, while 警察官 points more directly to an officer or officers.