Vampires can activate their third level obfuscate discipline and vanish from sight instantly, even where there are bystanders. Its stated that only those with supernatural powers, like Auspex, could see through the illusion unless the obfuscated vampire draws attention.
One of my players used this discipline to break into a museum and steal ancient tablets. The problem I'm having is, unsuspecting mortals are completely defenseless against this kind of burglary. Even the vampire has no skills to commit a heist, he can virtually never get caught, which eventually leads him to succeed.
During that scene, the vampire first tried to knockout the guard in the museum gallery and failed, shots were fired, alarms triggered. he immediately used cloak of night and vanished from sight. the mortal who got shot was panicked and confused of course, but he can't seem to understand how he was shot without anyone in the room. Next the vampire broke the glass that kept the tablet he came to acquire, and steal the tablets, mortals who came for the alarm draw their guns to shoot... and the vampire vanishes again.
Even they don't understand what they're up against, they initiated lock-down to all doors in the museum to keep the thief inside and wait for the police. The vampire waited patiently, used cloak of night before it expires again and when the police arrived he just get out whenever someone opens the door leading to exit. after a while he was outside, still invisible, with the tablet worth millions, and no clue left behind.
how am I supposed to counter that, not that I'm trying to foil all his plans, but if he keeps doing that, mortals have no means to stop him, and he might get too powerful or too rich too early.
Of course there is an option to plant supernaturals around valuable object and let them detect the vampire, but that should be my last resort, since it would be bending odds too far against the players.