The victims must have been quite close to their car, for her to be able to escape and come back.
IMO, the attacker probably had his car in the same lot - and committed the crime close to his car so he could quickly drive away - not go walking back through the park to his car, covered in blood, seen by more witnesses, etc.
So, I think the crime was fairly deliberate, in the sense he knew about his need to get away.
Also, he may have been hiding after the attack on the husband, waiting/watching for his chance to get to his car.
However, I think he didn't really know clearly what he was doing, since choosing 4 people was very foolish. A more deliberate killer would have lurked close to the park entrance until a solo person came by, and wouldn't have shown himself to others in the park.
JMO