[BleDrajor]

Well, I mentioned that with John some posts before. I'm confused about this, too. Especially because Nick said, that he talked to John before, what he didn't do, as you said.
John seems to be an old friend of Nick and a mechanic who built his ramp truck and this special truck you have to use for solving the mission.
(USA Trucker will look at this, maybe he finds out something...)

To the police:
Nick's wheel spider obviously had his finger prints on it. Jack Murdoc (Nick won a race for information against him.) was killed with this wheel spider. But Nick lent this thing to Crane.
(Later outside the police station Crance says, that he lent it to Matthew.)
Now Nick is the suspect because of his finger prints. Dakota was an unknown man until this moment. He is introduced later to Nick by calling and then meeting him in Oxnard. Dakota works for the state. That's why he acted concealed in the beginning until Nick meets him. He seems to be an undercover agent or something like that. Because Nick is an important person for Dakota and his case he contacts Nick and takes him out of the police station, no matter how he achieved that.