Sentence 1: Dave saw lights flashing behind him so he pulled his car over. 
 Sentence 3: Dave knew he wasn't speeding, but he was nervous anyway 
 Sentence 4:  Another cop came along and talked to the first cop 
 Sentence 5:  They had pulled over the wrong car and Dave was free to go 
 Given Sentence 2: The cop told him he was speeding.