How and why has Vernet's attitude changed and what does it mean for Langdon and Sophie in this section?

Vernet heard a radio report that Sophie and Langdon had killed three people. So, Vernet's attitude completely changed. Vernet held Sophie and Langdon at gunpoint, but they managed to escape. However, they don't know that Vernet activated a homing beacon in the armored truck. As a result, Interpol is able to continue following Sophie and Langdon fairly easily.