The use of a remote-controlled machine gun was not out of the question. Israel’s military has such weapons and has deployed them elsewhere. Some Iranian reports said as early as Saturday that such a weapon was used in the attack on Friday, an afternoon ambush on a country road east of Tehran.

But early official Iranian reports and witness accounts reported a gun battle between Mr. Fakhrizadeh’s bodyguards and as many as a dozen attackers. And current and former Israeli officials have boasted that Israeli intelligence agencies have a track record of safely extricating assassins from hostile territories, including Iran.

Israel is thought to have killed at least five Iranian scientists between 2007 and 2012 as part of an effort to derail Iran’s nuclear program, which Israeli officials consider an existential threat. Tehran has credibly claimed to have caught only one of the perpetrators, an Iranian who confessed on television in 2010 that he had received training in Israel to plant a car bomb that killed a scientist as he was leaving his garage.

The agents behind the other assassination attempts and some larger operations are all believed to have escaped.

The role of a remote-controlled machine gun as part of a complex attack by a team of assassins was first reported over the weekend in an account of the killing posted online by Javad Mogouyi, a documentary filmmaker for Iran’s Islamic Revolutionary Guard Corps. His father and father-in-law are members of the wing of the organization charged with protecting Mr. Fakhrizadeh, and Mr. Mogouyi’s account was adopted as authoritative at the time by several Iranian news organizations.

Before the arrival of a dozen assassins, Mr. Mogouyi wrote, a Nissan had been parked at a roundabout, packed with explosives and armed with an automated machine gun. The remote-controlled gun opened fire first, distracting Mr. Fakhrizadeh and his bodyguards as the assassins lay in wait.

An autonomous machine gun that appears to match that description has been employed by the Israeli military since 2010. Developed by Rafael Advanced Defense Systems, the weapon includes a built-in optical system for aiming and photographs. Its name, which rhymes in Hebrew, means “you see-you shoot.”