A rich man had been murdered in a certain part of the city. He was in his library at the time of the crime. His family was in an adjoining room, yet none of them heard any noise, or knew what had been done until they found him lifeless on the floor. Investigation proved that he had been shot, but not with an ordinary weapon. The missile in his heart was a combination of bullet and dart, evidently propelled from a powerful air rifle or spring gun. But no clew was left by the perpetrator of the crime, and Wooldridge carried the strange missile in his pocket for several months before a single prospect of apprehending the murderer appeared. Then it was the black cat that did it. What strange coincidence or freak of fate it was that impelled the cat to literally lead the detective to a little pile of dirt in an alley that night Wooldridge never has attempted to explain. But lead him it did, and when he dug into the disturbed ground he found something entirely new in the gun line, the weapon that had discharged the fatal bullet in his pocket. Eventually he traced the gun to its inventor, and from there to the man who had purchased it, a young fellow named Johnson, and a supposed friend of the murdered man's family. The consequence was that this man proved to be the murderer. When arrested he at first denied his guilt, broke down under the sweatbox ordeal and confessed, and--killed himself in his cell next morning. For mystery and good fortune in bringing an apparently untraceable criminal to justice this incident perhaps has never been equaled in Chicago's police records. ON DUTY IN GREAT STRIKE. In 1900 Chicago's great building trade strike occurred in which 60,000 men were thrown out of employment. Many acts of violence were committed. Several men were killed and many maimed and injured. Detective Wooldridge was placed in charge of thirty picked detectives from the detective bureau with orders to suppress these lawless acts and arrest the guilty offenders. Through his vigilance and untiring efforts law and order were soon restored, and he was highly complimented by Chief of Police Joseph Kipley and the public press. Literally speaking, the darkest situation into which his experiences have led him was the tunnel by which inmates of Mattie Lee's famous resort at 150 Custom House place escaped when the place was raided. Mattie had decided that it was a nuisance to go to the station every time the police wanted to arrest her, so she had the tunnel dug. After that when the police called on her Mattie greeted them with an empty house and a sweet smile, while underground the inmates were crawling on their hands and knees to safety. Wooldridge found the tunnel and, crawling in, "snaked out" six colored men and women whom he found in the darkness. Versatility is a requisite with the successful detective. REMARKABLE WORK AS A RAGPICKER.