LONDON — Questions about whether the British government could have done more to prevent the terrorist attack in London over the weekend mounted on Tuesday, two days before a national election, as new details emerged about the three men who carried out the deadly assault.

The authorities identified two assailants — Khuram Shazad Butt, 27, and Rachid Redouane, 30 — on Monday, and the British police on Tuesday confirmed the identity of the third as Youssef Zaghba, 22, an Italian of Moroccan descent.

The three men drove a rented van into a crowd of pedestrians on London Bridge late Saturday, and then used knives to attack patrons of pubs and restaurants in Borough Market. They were shot and killed eight minutes after the police were summoned — a rapid response for which the authorities have been praised. Seven people were killed. Of 32 people still hospitalized on Tuesday, 15 remained in critical condition.

Two former European intelligence officials, who spoke on the condition of anonymity because they were not authorized to discuss the case, confirmed that Mr. Zaghba had been stopped by the authorities at the airport near Bologna, Italy, in March 2016 while he was trying to travel to Turkey and on to Syria to fight for the Islamic State, also known as ISIS or ISIL. He was carrying an electronic device with Islamic State propaganda, they said.