Lonnie got a heads up from his mate about a Dedra running a tactical mission on Coruscant
He guessed it would be against luthen so he looked in her files (knowing they would find out, but he knows if Luthen gets interrogated he could be found out as well so may as well look then run for it) he then found out about the death star so "rang the big bell" to have crash meeting with luthen
tells luthen they will know he looked and be on to him
Luthen knows he has no time and must go now to trash the shop and get out - which he doesn't even really have time to do completely
There was no time to get Lonnie anywhere and Lonnie knows too much and would get captured to (and tell them secrets) - so he kills him
As soon as Luthen mentions Yavin there is no way he would do that (too risky) even if he wanted to take Lonnie there, he would just take him there (without saying where) he says Yavin to win Lonnies trust so he will tell him the info then kills him