I have never heard of LR asking for more tips or saying the tip lines are open after an arrest. There is something else going on. Jmoo Makes me kinda scared.
Maybe it's just that LE is thinking positively moving forward that with a name and a face now for the pubic to go on, and everyone in the area knowing he is someone who lives locally and not in some random location far away, it may jog someone's memory in a new way and more tips specific to him (the suspect BK) will come in to bolster what they already have.
For example, someone in his immediate circle of acquaintances (the university he attends or apartment building he lives in in Pullman) could remember something about the time around the murders that would go against his alibi, e.g., if it is "I was home sleeping, alone from 9 pm until the next morning when I went to the gym" and new witnesses came forward and said, e.g.,:
"oh yeah, his white car was not in its usual parking place late that night when I got home from the bars, so I got to park there" or
"he had bruises or scratches on his hands or face the next time I saw him after the murders" or
"I saw a guy who looked like him in Moscow that night in the neighborhood and he was ________"
Even if it's circumstantial, there could be credible witnesses that haven't come forward to "give context to the events of that evening" LE has been asking for until they knew who the suspect is.
I think LE does keep tip lines open after an arrest, oftentimes to gather more witness testimony and corroborate what they have, to eliminate or confirm if there were accomplices, etc., especially when it's a complex case like this with 4 murders committed without an obvious motive. MOO