PARIS — The gunfire had still not subsided, and those who could were running for their lives. But one man was crossing Paris to get close to the scenes of death.

Just after 10 p.m. on Nov. 13, the man, Abdelhamid Abaaoud, parked his rented getaway car in the eastern suburb of Montreuil, leaving behind the Kalashnikov he is believed to have used to shoot diners in central Paris a half-hour before. Apparently unconcerned as security cameras recorded his movements, he boarded the No. 9 subway line and returned to the part of the city that was still under siege. Before the night was over, investigators say, he had walked past the shattered cafes and bloodied concert hall that had been among his targets.

After a year of plotting terror in Europe but only producing four fizzled attempts, Mr. Abaaoud made sure this time was different. This time, he was on the scene, not directing from afar. This time, he monitored his team of assassins — old friends and new zealots — and surveyed the suffering. This time, investigators say, he had prepared for a second wave of assaults days later, and planned to die himself as a suicide bomber in the heart of the Paris region’s business district.

A foot soldier turned lieutenant in the Islamic State’s hierarchy, Mr. Abaaoud, a 28-year-old Belgian, had been under increasing pressure to deliver something big, Western intelligence officials say. “All these operations in 2015 had been failures, embarrassing failures,” said Louis Caprioli, a former deputy head of France’s domestic counterterrorism unit. “He needed to make sure this operation succeeds.”