Leon had spent the last while couped up inside, working. Or, he had been with D, working. He wasn't making too much headway either way, despite the fact that he was bouncing ideas off of D (Gumshoe might have been a cop, but he was also kind of an idiot).
So, he decided that he was going to mix things up a little. He really just needed a break.
Which brought him to laying in the grass near It's A Small World, using his teeshirt as a pillow, just enjoying the sun and the warmth. He also had with him a notepad and a pen. He was working.
((EDIT: FYI, Leon's... really scarred up. Not only does he have at least three or four scars from being shot in various parts of his body, he's also got several scars that look like
Animal bites or scratches))