This is a quote from a recent article with regard to the smell of gunpowder, I think by Colin McLaren, from the Australian Herald Sun newspaper:
"Patrolman Earle Brown was on duty. He had been allocated the south end of Elm Street and was standing with the crowd. He could see along Elm Street to Houston Street and, like the rest of those gathered, he watched with anticipation as the motorcade approached. His vantage point would prove the ideal location to see the tragedy unfold, looking straight down at the convoy of vehicles. He heard three shots and observed the President's limousine momentarily slow down before rapidly speeding up, ' ... then I smelled this gunpowder ... at least it smelled like it to me'. As the motorcade drew near, he noticed a Secret Service agent in the follow-up car. 'He had this gun and was swinging it around, looked like a machine gun, and the President was all sprawled out ...'
Alongside the patrolman stood two co-workers, mail clerks Royce Skelton and Austin Miller. Royce heard the first two shots as the President's car was travelling towards him. 'I thought that they were dumballs [sic] that they throw at the cement because I could see smoke coming up from the cement ...' Austin Miller believed the shot or shots ' ... sounded like it came from the, I would say from right there in the car ...' Miller also said he ' ... saw something which [he] thought was smoke or steam ...'
Railway switchman Walter Winborn was also standing on the Elm Street overpass. He saw smoke, ' ... it looked like a little haze ... but it was a haze there ... at least ten feet long and about two or three feet wide ...'
Motorcycle cop Bobby Hargis, who was riding alongside the President's car, said ' ... I was staying pretty well right up with the car,' which puts the police officer among the closest persons to the President at the time of the assassination attempt. Hargis believed the shots had come from 'behind' him, ' ... sounded like the shots were right next to me ...'
Officer Martin, on motorcycle duty on the left side of the President's convertible, was close to Mrs Kennedy. He recalled, ' ... you could smell the gunpowder ... you knew he wasn't that far away. When you're that close you can smell the powder burning ... Why, you can smell the gunpowder ... right there in the street.'
Patrolman Joe Smith also smelled gunpowder, ' ... a distinctive smell of gun smoke cordite,' as he moved along Elm Street towards the grassy section of Dealey Plaza.
In my investigator's brain, alarm bells had started to ring. As I trawled through the many hundreds of pages related to the witnesses' observations from the overpass and on the street closest to the President's vehicle I could sense a pattern forming, and detectives love finding evidence of similar facts. Not only is it corroboration, but it helps to understand exactly what happened at a crime scene. Here was sworn testimony from a supervisor, several police officers and two mail clerks telling me, the reader, that smoke or gunpowder was on the street in or around the President's vehicle. Extraordinary! I delved deeper and kept reading, remembering the old adage, where there's smoke, there's fire."