Why did the police stop lefty Lewis car In bud not buddy?

In "Bud, Not Buddy" by Christopher Paul Curtis, the police stopped Lefty Lewis's car because they were investigating a case involving a stolen vehicle. Bud, the protagonist, was initially anxious about the situation, but Lefty defended himself and his passengers, which ultimately helped Bud feel safe. This encounter also plays a significant role in the development of Bud's journey as he seeks his father.