Tensions come to a head between the detective and potential killer when they are chained together. Light doesn’t have her memories, so there can be no confirmation that she was or wasn’t Kira. The working theory is that somehow she was possessed, but they don’t even know by what. Being around L is taxing enough for anyone. But being chained to her while also under constant scrutiny and interrogation is driving Light up the wall. There have been numerous fights already. The task force mostly ignores their arguments now.