kono shashin ga tegakari ni natta.

This photo became a clue.

Breakdown of kono shashin ga tegakari ni natta.

• が: subject particle
• 写真しゃしん: photo
• この: this
• なる: to become

Questions & Answers about kono shashin ga tegakari ni natta.

What is the basic grammatical structure of この写真が手がかりになった?

The structure is:

• この写真 = this photo
• が = marks the thing being focused on
• 手がかり = clue, lead
• に = marks the result/state after a change
• なった = became

So the pattern is:

A が B に なる = A becomes B

In this sentence:

この写真が手がかりになった
= This photo became a clue
or more naturally, This photo turned out to be a clue / This photo served as a clue.

Why is が used after 写真 instead of は?

が highlights this photo as the thing that became the clue.

So the sentence has a sense like:

• It was this photo that became the clue
• This photo is what served as the clue

If you used は instead:

この写真は手がかりになった

that would sound more like you are introducing this photo as the topic and then commenting on it: As for this photo, it became a clue.

Both can be possible in context, but が is very natural when identifying or focusing on the specific thing that played that role.

What does に mean here? Is it the same as location or destination?