Why did Light have to kill 23 lesser criminals during the period Dec 19 to Dec 27?

Question

In Episode 6 ("Unravelling") of Death Note, L reveals that during an 8-day period from Dec 19 to Dec 27, Kira deviated from his usual behaviour by killing 23 "lesser" criminals, and that the reason why he had to kill so many was so that the police wouldn't know which ones were actually used for his plot to kill the FBI agents.

However, we also learn during this episode that nobody other than Light and Naomi knows that Kira has the ability to kill his victims using causes of death other than heart attacks. Since the bus-jacker Light used to learn Raye's identity didn't die of a heart attack, this means Light should have known that the police would not think to link the bus-jacking incident to Kira. If that's the case, then why did he have to kill those 23 other people? As a matter of fact, his doing so allowed L to deduce that an FBI agent met Kira prior to the start of that period. If he hadn't killed those 23 people in that 8-day period, L wouldn't have any reason to suspect this.

So why did Light have to kill the 23? Wouldn't he have been better off carrying out the whole plot with Raye but without that detail?

Answer 1

There are a few reasons that come to mind:

1. To cover over the death of the lesser criminal he used as proof: In Episode 5, when kira confronted Raye, he killed a lesser criminal wearing glasses in front of a coffee shop who was alleged of sexual crimes to demonstrate to Raye that he is really Kira. It stands to reason that Kira, being as cautious as he is, would kill 22 other lesser criminals as decoys to cover that one.
2. To conduct more tests: He needed to experiment on the death note more in that period that the number of convicted criminals probably wasn't enough, so he needed more test subjects. Also, the lesser criminals, being free, provide more useful feedback than the jailed ones (you can't make a test subject hijack a bus from inside a prison cell). In Episode 5, Kira told Ryuk that he can write the time and circumstances of death first then add a name later and the death will still happen, the test subject for this particular experiment died on December 26 by a car accident. The reason for their death probably wasn't originally a heart attack, the heart attacks could be due to the impossibility of the tasks they were given (like the prisoner who was meant to die in front of the Eiffel Tower in Episode 4). Also, bear in mind that he may have killed some of them as decoys to hide the real test subjects.
3. As red herring: To keep L and the Police busy elsewhere while he was planing to kill the FBI. He even used some of the convicted inmates for that purpose by making them write encrypted messages to L.