Director Laura Belsey and cinematographer Michael McDonough came up with the shot after Bosch informs the Skylers of Borders' arrest, which pulls back from the window of the house to Bosch sitting in his car in the present day, transitioning from B&W to color along the way.
When Bosch and Jerry Edgar are talking at Jerry's cubicle at PAB (police administration building) there is a picture of J. Edgar's boy with a push pin through his forehead. No cop would put a hole in the picture of a loved one, especially a Homicide Detective. Call it superstition. The pin would be off to one side or has two pins, one in each corner. Not through the loved ones body.
"Bosch" hasn't trafficked much in flashbacks before now, but episode 504 has three of them, shot in black and white. The first is Bosch at the Danielle Skyler crime scene; the second is the finding of the pendant at Borders' apartment; and the third is Bosch informing the Skyler family of Borders' arrest.
The movie that Barrel (Troy Evans) watches with his dog is "Man Without a Star," starring Kirk Douglas. Episode writer Tom Bernardo chose this film because he used to watch it a lot with his father, who was a huge fan of Westerns.
Bosch uses his own military background and widower status for his backstory when he's undercover as Reilly. He doesn't have time to work up a complete false history but doesn't think he'll have to be undercover for long.