Jerusalem (CNN) Israeli Prime Minister Benjamin Netanyahu was questioned "under caution" in Case 4000, according to an Israeli official, making him a suspect now in three corruption investigations.

Investigators questioned Netanyahu at his residence in Jerusalem for five hours Friday morning, marking the eighth time the Israeli leader has been questioned in graft probes targeting him and his inner circle.

An Israeli official told CNN that Netanyahu was questioned "under caution," which refers to the questioning of someone suspected of having committed a crime, with the warning that anything they say, or decline to talk about, could be used against them in court proceedings.

A video image showing Israeli police at the entrance to Benjamin Netanyahu's home on Friday.

Police simultaneously interrogated Netanyahu's wife, Sara, at a different location. She too was questioned "under caution" in Case 4000, the official said. Her lawyer also confirmed those details to Reuters.

Case 4000 is one of the biggest investigations facing the Israeli leader, dealing with the relationship between the Ministry of Communications -- at a time when Netanyahu was the Communications Minister -- and Israeli telecommunications firm Bezeq.

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