The fact of the matter is that the police were virtually worthless in this case. It was civilian witnesses who reported the blue Caprice, it was civilian radio talk show hosts who reported the car to the public (while the police wanted the news suppressed), and it was civilians at a rest stop who blocked the car in with their trucks. If civilians had been allowed to carry guns as well, they could have made the arrest, too.
BTW, when Muhammed lived in Tacoma, Washington, his neighbors called the police, complaining that he was target practicing with a rifle in his back yard. The police did nothing. Which is why Muhammed became the Beltway Sniper, instead of sitting out 2002 in jail.
And they didn't have any suspects in the shooting of the young woman in Washington state--the babysitter, I do believe--until after Mohammed and Malvo were arrested. The woman who lived in the house where the young woman was shot was the woman who helped Mohammed's ex-wife get her children back after Mohammed took them to Antigua. For some reason, the police didn't make the connection between the shooting and Mohammed until there was a ballistics match.