You must truly understand the company's philosophy. BlackRock prides itself on being fiduciary. Behavioral questions will try to gauge if you understand how the firm is different than most asset managers. Also, having a basic understanding of BlackRock's Aladdin technology will help. It's something the firm prides itself in.
I applied online. The process took 2 months. I interviewed at BlackRock in Jan 2015
Interview
Mostly behavioral, lot of discussion around the resume. A number of technical questions regarding the role. Back and forth questioning. Great interviewers - they were all very engaging and helpful