I looked at that and if he even a small bit more careful, I don't think they could catch him...
1. If he wore a beard and unidentifiable cloths which he bough in a large retailer.. You have to be unrecognisable to your mother but not seem like you have a disguise on either...
2. Disposes of his weapon and clothes properly
3. Swaps cloths during escape outside cameras
4. No Phone or any other electronic device
5. Everything use has to be untraceable
6. Don't go to a fire range to learn how to shoot...
You have traffic & co cameras which are the main reason you are getting caught... You have disrupt the sequence so you are unrecognisable when you come back on...
Right over thought that completely....
Wear latex gloves and booties over your shoes. Carry a bag with Clorox wipes to destroy any DNA evidence you may leave behind. Be sure any phones or computers you have are formatted or destroyed ahead of time. Remove as much information on the cloud as you possibly can. Have an alternative means of transportation to immediately leave the area. Don't be cute and write anything on bullets or leave manifestos.
Be sure you have a weapon that can easily be left at the scene that cannot be tied to you or anybody you know, and is thoroughly Clorox cleaned when you leave it.
Don't burn clothes. DNA can still be recovered. Not out of a bucket of bleach and water though. Even if small amounts of DNA can be recovered, bleach alters it to the point a defense attorney can get expert testimony that has it excluded from discovery.
Don't be seen in stores buying ammunition. You're going to be seen on cameras from some angle. A simple N-95 mask, and a Tyvek suit used by the construction industry is the easiest, and cheapest disguise you can use, and very easily disposed of. You can take it off and put in your pocket.
Getting away with an assassination is comically simple, and the FBI showed everybody that yesterday by releasing the photo and video evidence they did, because they had zip until daddy turned him in. Just a few extra precautions, and he would have absolutely gotten away clean.
And have no illusions in your mind. They were scared shitless this guy was going to get away, and all of the huffing and puffing was never going to catch him, if he had been just a bit more careful.