That's usually how it works. Progress from relatively harmless petty crimes like shoplifting and minor theft to more violent things like assault, robbery and perhaps even low grade sexual assault. Finally either the compulsion is too strong or an abduction/SA goes too far and they take the final irreversible step. Many who are in the same boat as this guy have said "they weren't" when asked what were you thinking when you actually committed the murder.
Unless this guy is a serial killer - which based on his history, planning and seeming intelligence level I seriously doubt - the act of murder is almost always to eliminate evidence. Deceased people can't tell their story so the murder and body disposal is a vehicle to further that and yes, most criminals are sincerely dumb enough to think they can get away with it.