"Scarface" with Al Pacino as Tony Montana features a scene where Bolivian kingpin Sosa kills Tony's colleague Omar, saying Omar was an informant.
Later, back in Miami, an angry Frank Lopez tells Tony that Sosa was lying.
What was the truth?
The answer is No! Omar was not an informant. Sosa killed Omar because he knew if he let Omar go back to Miami that him and Frank would never make the deal. He could tell that Omar knew Frank wouldn't be interested in a deal that big. But he knew Tony would be and that if he sent Tony back alone that the deal would most likely get done. If not, he would kill them just like he did Omar and as we all know later on Tony as well. Frank was just surprised and disgusted that Tony tried to make the deal himself and suddenly was so enamoured with Sosa who he already didn't care for. As you saw throughout the movie Sosa did away with pretty much anyone who stood in his way with making $ .
It is not shown, nor implied in the movie whether Omar really was an informant. However, given the situation, the logical answer to the question seems to me to be yes.
If Omar really was an informant, would Frank really have known about it? Of course not! Frank's denial or reply that Sosa was lying had more to do with his anger at that moment. Tony had just come back with an unauthorized deal with Sosa without Frank's nod and claimed that they killed Omar(who was Frank's man) because he was an informant. Obviously, Frank went in denial. So as a personal opinion, yes it looked that way. Omar was an informant.