tantousya wo tokuteisita.

It is read:

たんとうしゃ を とくていした
tantōsha o tokutei shita

In natural speech, を is usually pronounced o, even though the kana is written を.

担当者 means the person in charge, the person responsible, or the 담당 staff/member, depending on context.

It is made of:

• 担当 = charge, responsibility, assignment
• 者 = person

So 担当者 is literally the responsible person or the assigned person.

を marks the direct object of the verb.

In this sentence, 担当者 is the thing/person that was identified, so it takes を.

Structure:

• 担当者 = the person in charge
• を = direct object marker
• 特定した = identified

So the grammar is basically:

[object] を [verb]

特定した is the past plain form of 特定する.

Breakdown:

• 特定 = identification / specification
• する = to do
• 特定する = to identify, to specify
• 特定した = identified

So this is a plain past verb form, meaning the action has already happened.

Japanese often leaves out the subject when it is understood from context or not important.

So 担当者を特定した does not explicitly say:

• I identified
• we identified
• they identified
• the police identified

The listener is expected to figure that out from the situation.

This is very normal in Japanese.

It is plain style, not polite style.

That does not necessarily mean it is rude or casual in tone. Plain style is also common in:

• written reports
• news-like summaries
• notes
• internal descriptions
• narrative writing

If you want a polite version, you could say:

担当者を特定しました。

特定する has a more precise, analytical nuance than 見つける.

• 見つける = to find
• 特定する = to identify specifically, to determine exactly who/what it is

So 特定した suggests something like:

• determining exactly which person it was
• narrowing it down
• confirming the identity

It often sounds more formal, technical, or investigative.

Yes, depending on context, that nuance can be present.

Because 特定する often means pinpoint or determine exactly, the sentence can imply that out of multiple possibilities, someone figured out exactly who the responsible person was.

So it is not just noticed or found; it can suggest successfully determined the exact responsible person.

This is a very important difference:

• 担当者を特定した = identified the person in charge
• 担当者が特定した = the person in charge identified (something/someone)

So:

• を marks what was identified
• が marks who did the identifying

Changing the particle completely changes the role of 担当者 in the sentence.

No, normal Japanese is usually written without spaces:

担当者を特定した。

Spaces are often added in learning materials to make the structure easier to read. They are not normally used in standard Japanese sentences.

It can stand by itself grammatically, but in real use it often depends on context.

For example, a reader may still wonder:

• Who identified the person?
• Which person in charge?
• In what situation?
• How was the identification made?

Japanese often allows short context-dependent sentences like this, especially in:

• reports
• summaries
• headlines
• procedural descriptions

So the sentence is complete, but context usually fills in the missing details.

The non-past plain form is:

担当者を特定する。

This can mean:

• identify the person in charge
• will identify the person in charge
• identifies the person in charge

depending on context.

The polite non-past form would be:

担当者を特定します。