Too Late To Back Down Now
Gray specifically waited until Aaron was out of town to execute his plan to kill Lacy. He knew his brother wanted her gone but he also knew that if he had an idea what Gray was up to that he would put a stop to it.
It was time for her to die. Not only was she a total psycho who would never leave the Hale family alone, she was preventing Aaron from finishing his plan to kick Alistair out of the company.
Gray had been watching and waiting for years to see that gloriousness unfold. Once again, that shrew was annoyingly in the way. No one liked her anyway. He was doing the whole world a favor.
That she thought she could trick him was laughable. Did she really think he hadn't noticed the camera she planted in his office? It wasn't even that cleverly hidden.
The 'accident' was all set up and ready to go but the people he had paid to do this weren't available until tomorrow. No matter. He had waited this long, he could wait a little longer.