Police are investigating a complaint by water company Gal-Al that a rival firm stole drawings and formulas on how to produce and separate heavy water in a project at Israel's Dimona nuclear reactor.

Producing and separating heavy water is needed to manufacture a hydrogen bomb. Israel has never admitted having a nuclear arsenal, but is widely believed to have around 200 nuclear warheads.

Gal-Al director Baruch Zisser refused to make any comments on the case on public radio.

Twenty people, including top business executives, have been arrested in an unprecedented industrial espionage scandal in Israel that has so far implicated 15 companies -- including some of the most prestigious in Israel.

Evidence gathered by the police shows among those infiltrated were car importers, television stations, PR firms and telephone companies, to track all actions carried out in the system and even to control the computer remotely.

The investigation has spread from Israel to Britain, Germany and the United States.

On Wednesday, a key Israeli suspect in the hacking scandal, Yitzak Rath, fell from the second storey of a police station after undergoing a lengthy interrogation in what police believe was a suicide attempt.

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