Police detained six people for questioning on Monday morning, including a number of former senior public officials, suspected of corruption in the potentially fraudulent purchase of naval vessels from Germany.

The suspects were brought in as part of an ongoing investigation into the so-called “Case 3000,” or the “submarine affair,” in which Prime Minister Benjamin Netanyahu’s personal lawyer David Shimron is suspected of attempting to sway multi-billion-shekel deals in favor of the German shipbuilder ThyssenKryupp, which he represented in Israel.

The six were questioned under caution over suspicions of fraud, bribery, tax evasion and money laundering, the Israel Police and the Tax Authority said in a joint statement.

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“At the time of the events under question, some of the suspects were public servants and some worked in the private sector,” the statement said.

A source close to the investigation who asked not to be named told The Times of Israel that some of the suspects were personal associates of the prime minister. Hebrew media speculated that Shimron was among those being questioned.

One of the detainees was named later Monday as Avriel Bar-Yosef, a former deputy head of the National Security Council. Netanyahu sought to appoint Bar-Yosef to lead the NSC in 2016, but his candidacy was withdrawn when it emerged that he was suspected of accepting bribes in exchange for promoting the interests of German businessmen involved in the development of Israel’s offshore gas fields

Attorney General Avichai Mandelblit ordered the Israel Police to formally look into the submarine affair in November 2016, after accusations surfaced that Netanyahu may have been swayed to purchase vessels by business ties Shimron had with ThyssenKrupp. The deals for patrol boats and submarines came under intense scrutiny late last year after it was revealed by Channel 10 news that Shimron also served in an advisory capacity for ThyssenKrupp, which was awarded the contracts for building Israel’s submarines and naval attack boats.

In December, officers from the Lahav 433 police anti-corruption unit entered the office of legal adviser Ahaz Ben-Ari at the Defense Ministry building in Tel Aviv and removed information from computers there. The data concerned the cancellation of an international tender to build four new warships to protect Israel’s offshore natural gas rigs in the Mediterranean Sea.

The contract was awarded instead to ThyssenKrupp. Under the 2015 deal, worth €430 million ($480 million), ThyssenKrupp is to supply Israel with four “Sa’ar 6 corvette” ships over a period of five years.

The purchase was opposed by parts of the defense establishment, including then-defense minister Moshe Ya’alon, who has since threatened to “tell all” on Netanyahu’s involvement if the prime minister is not indicted as part of the probe.

Shimron claimed at the time that he “wasn’t in touch with any state official over the issue of Israel’s purchase of naval vessels” and said that his work for the German company while also serving as the prime minister’s lawyer did not constitute a conflict of interest.

However, after Israel issued the initial tender in 2014 for the purchase of the ships, Shimron called Ben-Ari, the Defense Minister legal adviser, to inquire why the tender was issued, allegedly saying he wanted the contract to be given to ThyssenKrupp directly.

In January, police opened a full criminal investigation into the affair but stressed that the prime minister was not a suspect.

Responding to the decision, the Prime Minister’s Office published what it said was the full timeline of the process by which the state decided to purchase submarines from a German shipbuilding company, in an effort to demonstrate that Netanyahu did not attempt to influence the deliberations in any way.