James Blenkingsop was a night watchman on duty in St. James Place, near Mitre Square, on 30 September 1888. He gave a short statement to the Star in which he described an encounter he'd had with a man at about 1.30am (approximately 14 minutes before the discovery of Eddowes' body in Mitre Square):
James Blenkingsop, who was on duty as a watchman in St. James's-place (leading to the square), where some street improvements are taking place, states that about half-past one a respectably-dressed man came up to him and said, "Have you seen a man and a woman go through here?" "I didn't take any notice," returned Blenkingsop. "I have seen some people pass." (Star - 1 October 1888)
Blenkingsop is nowhere to be found in the surviving police records, nor was he present at the Eddowes inquest. Many modern researchers wonder why Blenkingsop was, apparently, disregarded by the authorities.
Sugden suggests that Blenkingsop may have been wrong in estimating the time, and that his encounter makes much more sense if it were to have taken place sometime after 1.44am. If that were the case then the man he spoke with may very well have been a plain-clothes detective investigating the still-fresh crime.
Star - 1 October 1888
Complete History of Jack the Ripper (Sugden)