Money for drugs and mafia funds are often rewards for murder.

Literal

Drugs [purpose-のための] money [and-や] mafia [possessive-の] funds [topic-は] murder [possessive-の] reward [copula-である] thing [subject-が] many.

~であることが多い ('it is often the case that') combines the formal copula である with ことが多い ('often'). The sentence strings together multiple の-linked compounds in a formal, news-like register.