The Camarilla, shortly after its founding, declared war on the Assamites, and forced upon them the Treaty of Tyre, which included a terrible curse, making the Vitae of other Kindred poisonous to them and effectively stopping their tendency to diablerize members of other clans almost upon sight. Other highlights of the treaty include never leaving Alamut (their fortress/domain/mountain) and removing all of its fortifications.
The curse they turned into a weapon, since their own Vitae is now poisonous to other Kindred3); they removed all of Alamut's fortifications, but Alamut itself promptly disappeared; and as for never leaving it… they have topped their mad assassination skillz with equally mad espionage skillz and have infiltrated vampire society to the max. If no one else can help you, and if they want you to find them, maybe you can hire an Assamite.
It is said that they accept only one for of payment - blood.
It is also said that if an Assamite tries to assassinate you and fails, no Assamite will ever try again. There are not enough cases for viable statistics.
Following their tracks to India, the party found Alamut and a big chunk of the module.