Why didn't L arrest Light after he regained his memory?
I just want to say that having no memory of committing a crime isn't a "get out of jail free" card. It wouldn't even get you labeled as criminally insane and sent to an asylum.
When Light lost his memory, there was a time where L asked him something like, "Knowing what you know about this case, your own capabilities, the fact that at one point Light Yagami confessed and turned himself in, then he and the other suspect seem to have suffered from a personality change resulting in memory loss, would you assume that Kira has made Light Yagami lose his memory or that he lost his memory on his own free will?"
Light paused and was like, "Well... I'd have to assume that Light chose this."
With something like that, I think L would have investigated this memory loss situation deeper and probably found out how it worked. I mean, it was suspect from the start. When Light tried to call Misa during the situation where L touched her butt at their college, that was a red flag, the prime Kira suspect secretly tried to contact the prime second Kira suspect, who could kill just by seeing a face, immediately after she saw L's face. Then all of the sudden both suspects suffered severe memory loss which made them seem innocent. That was way too convenient!
Still, why didn't L investigate further and arrest Light?
When Light lost his memory, there was a time where L asked him something like, "Knowing what you know about this case, your own capabilities, the fact that at one point Light Yagami confessed and turned himself in, then he and the other suspect seem to have suffered from a personality change resulting in memory loss, would you assume that Kira has made Light Yagami lose his memory or that he lost his memory on his own free will?"
Light paused and was like, "Well... I'd have to assume that Light chose this."
With something like that, I think L would have investigated this memory loss situation deeper and probably found out how it worked. I mean, it was suspect from the start. When Light tried to call Misa during the situation where L touched her butt at their college, that was a red flag, the prime Kira suspect secretly tried to contact the prime second Kira suspect, who could kill just by seeing a face, immediately after she saw L's face. Then all of the sudden both suspects suffered severe memory loss which made them seem innocent. That was way too convenient!
Still, why didn't L investigate further and arrest Light?