Last year the Surpreme Court of the United States ruled that what he did was not legal:
A routine traffic stop is more like a brief stop under Terry v. Ohio, 392 U. S. 1, than an arrest, see, e.g., Arizona v. Johnson, 555 U. S. 323, 330. Its tolerable duration is determined by the seizure’s “mission,” which is to address the traffic violation that warranted the stop, Illinois v. Caballes, 543 U. S. 405, 407 and attend to related safety concerns.
Authority for the seizure ends when tasks tied to the traffic infraction are—or reasonably should have been— completed.
The Fourth Amendment
may tolerate certain unrelated investigations that do not lengthen the roadside detention, Johnson, 555 U. S., at 327–328 (questioning); Caballes, 543 U. S., at 406, 408 (dog sniff), but a traffic stop “become
unlawful if it is prolonged beyond the time reasonably required to complete the mission” of issuing a warning ticket, id., at 407.
My goodness how long did this one go on? He can be charged probably on this alone---
http://www.supremecourt.gov/opinions/14pdf/13-9972_p8k0.pdf