Why did CBI launch an investigation into Todd Johnson's death and not Rebecca Anderson's?

Question

In season 2, episode 8 of the Mentalist, it is revealed that Rebecca Anderson, a secretary in CBI is a Red John operative. She kills a number of CBI agents, etc. After Patrick questions her, she is escorted to a holding cell. On the way there, she is poisoned and dies. The person who poisons her walks right past the officer escorting her to the holding cell.

Compare this with Todd Johnson's murder. He was discovered to be a cop killer (just like Anderson). Patrick refuses to question him, even though Johnson requests to talk to Patrick. Patrick eventually goes to talk to Johnson and finds him on fire in the interrogation room. In the hospital, Johnson's last words to Patrick were "Tyger, Tyger", revealing to Patrick that he too was a Red John operative.

Now, compare the CBI response to both of these killings. With Anderson, they knew she was a Red John operative and she was killed in their custody. CBI does nothing to investigate her death that we are aware of. With Johnson, only Patrick knows. CBI puts JJ LaRoche in charge of investigating his death since there is a murder in the CBI. This investigation plays a significant role in a number of episodes through out the season. Patrick himself is very interested in knowing who the killer was since that leads him to Red John.

Why did they not investigate who killed Anderson? Why wasn't Patrick interested in knowing who had killed her?

Patrick realized she was poisoned due to the very visible marks on her hands, foaming of the mouth, etc. The guard walking her to the holding cell must have seen who walked past seconds before she dies. Furthermore, they could have tested her to figure out that the poison was fast acting, meaning she didn't poison herself hours before, etc.

Answer 1

Remember, they only show us stuff that's interesting and plot-relevant. I'm sure Patrick Jane eats lunch every day, but they rarely bother to show it on camera (unless he's meeting someone to discuss Plot Details.)

Why did they not investigate who killed Anderson?

Logically, there would have been an investigation, of course. There would always be an investigation whenever a prisoner dies in custody. They didn't show it on screen because it didn't contain any relevant plot details or drama. She got killed, we don't know who did it, it was probably another RJ cultist.

Compare this to Johnson's assault, which was particularly spectacular, and Patrick Jane was the last known person to visit him in custody, to boot. Investigating Jane as the prime suspect in the attack makes for good drama, hence they brought in LaRoche and did it on camera.

Why wasn't Patrick interested in knowing who had killed her?

Throughout the course of the show, Patrick's only REAL interest is finding Red John and exacting his revenge. He went to visit Johnson in the hospital because Johnson was still ALIVE and therefore might talk (which he sort of did.)

Anderson was dead before she hit the floor. Patrick examined her corpse for clues, but didn't find anything to go on. Thus his interest in her ended.

The guard walking her to the holding cell must have seen who walked past seconds before she dies.

Not necessarily. The killer was wearing a police uniform, which would help him "blend in" and the officer escorting Anderson had a very distinct "thousand yard stare" going. He never looked directly at the killer during his approach, so as long as the killer's face was nondescript, the escorting officer may not have been able to describe him very well. (We do know that his face was uncovered, because Anderson saw him and smiled, so she recognized him.)

There were also several other people in the hallway around Anderson and her escort when she collapsed, so it wouldn't necessarily have been obvious that the uniformed individual who passed her was the one who poisoned her. And, of course, he was long gone before they could lock down the area.

Furthermore, they could have tested her to figure out that the poison was fast acting, meaning she didn't poison herself hours before, etc.

The fact that she was murdered would not have been in question, however, finding evidence was apparently not so straightforward. The fact that the show never bothers to follow up on this investigation (which, again, must have happened, logically) further suggests that nothing useful came of it.