You underestimate the effectiveness of the natural cover and overestimate the DC police's search effort.
Eventually a trail-wanderer brings a dog in the area who finds the remains. The only reason he didn't kill the first victim seems to be that he thought someone was coming. The only reason he didn't kill the first one after he got her off the trail with a hand over her mouth, is that she got away.
She felt him relax (he's subdued her with a knife and gotten her to shut up) for a moment, and bolted away. She was in good shape and lucky - he didn't catch her.
Chandra was a tiny girl. He might have hit hard in the head her to make her shut up. If he dragged her down a ravine, too, she might have been injured and less able to resist.
A man with a knife doesn't inflict any bodily harm on either of two victims, despite the fact that he's already supposedly killed one before that? He rolls down the hill with one, a knife at her throat, and the story doesn't mention that there were any wounds?
Murderers are dangerous fugitives because once they've killed, they have nothing to lose by killing again -- yet this guy didn't even inflict any serious wounds on his next two victims? There's no physical description of the two victims, BTW, so comparing them to Levy's physique is a non-starter -- for all we know, they were as petite, or more so, than Levy.