From the extensive Timeline page at "The Great Rebellion: A Socio-economic Analysis of the 1967 Detroit Riot"

Sunday - July 23 1967 3:45 a.m. Detroit police "clean-up squad" raid a blind pig (speakeasy) housed at Economy Printing, 12th Street/Clairmount. Angry crowd of locals begins to form outside, eventually numbering some 250 people. 4:05 First paddy wagon loaded and departs for 10th Precinct. 5:00 D.P.D. departs with last prisoners under hail of projectiles. 5:05 Mob flows down street breaking windows. When police do not reappear, looting begins. 5:06 Tenth Precinct's Lt. Raymond Good investigates complaint of "burglar alarms going off on 12th Street." 5:11 Lt. Good arrives at Economy Printing and witnesses swarms of crazed people. When he exists the cruiser to get a better look he is hit with a brick. Good radios all cruisers to stay out of area in hopes that rioters will cool down faster without a inflaming police presense. 5:20 Police Commissioner Girardin notified there is a flare up on 12th Street. Girardin notifies Mayor Cavanagh. 6:00 Detroit police begin calling in off duty officers. Strength bolstered to 369 men but only 43 committed to riot area. 7:50 Detroit police Commandos conduct sweep of 12th Street but proves ineffectual. At least 3,000 rioters present. Belle Isle closed. 8:24 First fire is started. Detroit Fire Department arrives and extinguishes fire without incident. All police leaves canceled. Twelve hour shifts ordered. 9:00 Crowd on 12th Street now between 8,000 - 10,000. 9:33 Black community leaders attempt to calm thousands of rioters on 12th Street and are stoned in return. 10:00 Police strength now 1,122 men, approx 1/4 of department. Of these, 540 sent to riot area, 108 attempting to cordon off streets entering riot area. 10:30 Police now find themselves under a barrage of bottles/stones. Character of riot is changing from carnival atmosphere to violence. . . . . Main page: http://www.detroits-great-rebellion.com/Index.html