Maria Cramer

It was unclear when the information arrived, or whether it would have helped speed an arrest in the death of Brian Thompson, the chief executive of UnitedHealthcare.

Three days after an insurance executive was fatally shot on a Manhattan sidewalk, the authorities provided a detailed timeline of the suspect’s movements. It was not yet known what was in the backpack.

Investigators have begun to piece together the actions of a man they believe killed a health care executive on a city sidewalk early Wednesday morning.

Cameras are everywhere in Manhattan and they helped lead investigators to a distinctive backpack in Central Park that could be a key piece of physical evidence.

The prelude, the crime and the aftermath were all caught on video. But investigators will need to use human intelligence to find the person who gunned down an insurance company’s chief executive.

Peter Dering, the founder and chief executive of Peak Design, says he called the N.Y.P.D. tip line on Wednesday after receiving a wave of messages showing the suspect carrying a distinctive backpack.

Words including “delay” and “deny” appear to have been inscribed on casings collected after Brian Thompson was shot outside a Midtown hotel.

The gunman is still at large, the police said, and the victim is in stable condition. The episode left New Yorkers sheltering on subway cars and led to delays across the transit system.

Commissioner Thomas Donlon and his acting chief of staff, Tarik Sheppard, had to be separated by another official, said people familiar with the dispute.

Madison Square Garden, where former President Donald J. Trump will hold a rally on Sunday, has hosted many political events, some of them notorious.