(JTA) — Polish authorities are investigating whether the men who blew up a bus of Israeli tourists in Bulgaria bought the bomb’s detonator in Warsaw.

Maciej Kujawski, a spokesman for Poland’s attorney general, confirmed to Polskie Radio on Monday that Poland is assisting Bulgaria in investigating the bombing which killed five Israelis and a Bulgarian in Burgas on July 19, 2012.

According to Polskie Radio, parts of the bomb were acquired in Warsaw.

The Bulgarian Trud newspaper reported on its website that three individuals, including the unidentified bomber who was killed in the attack, were in the Polish capital on June 28, 2012, 20 days before the blast, on a bus taking tourists from the local airport to their hotel.

The three men arrived in Warsaw by train and purchased a detonator and a remote control device which they smuggled back into Bulgaria, according to the Trud report.

Bulgaria’s interior ministry have identified Lebanese-born Australian Meliad Farahalso, also known as Hussein Hussein, and Lebanese-born Canadian Hassan El Hajj Hassan, as two men involved in the bombing.

All three men have been identified by Bulgarian police as being members of the military wing of Hezbollah.

Bulgaria’s Interior Minister Tsvetlin Yovchev said in February that there were “clear signs that say that Hezbollah was behind the bus bombing.”

Last week, the European Union designated Hezbollah’s military wing as a terrorist organization. Hezbollah denies involvement in the Burgas attack.