They do say

警察庁によると、モネロを分析し容疑者を特定したのは日本では初めて。

"According to the police, this is the first time in Japan a suspect has been identified by analyzing Monero."

but they say later in the article

仮想通貨の流れを解析し一連の犯行に関与した疑いが強いと判断した。

which is like

"analyzing the flow of cryptocurrency they became strongly suspicious of his involvement in the many crimes"

iow, not Monero specifically.

but its useless to speculate...

could be a lie.

probably timing analysis moving to and from BTC or ETH.

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