If the police were looking for the Jeep, then the "fugitives" should take it with them is what I thought. The point of separating the groups is that Sam & co. can go meet the smugglers without being bothered by the police. If they see the Jeep without the people they want, the police would at least bring you in for questioning. At least that's my reasoning. Then again, if that's not the case, Clementine would know since she has some law enforcement procedures knowledge.