Moo is that yes, Todd is an extremely scrawny size and in many different ways such a murder/disposal would be extremely difficult, if not impossible to complete all alone without any assistance..
But IMO to the contrary there IMO are several different ways in which its absolutely possible to complete the murder/disposal all alone and without any assistance..
Long ago I stated my opinion about Katrina's car being the main and sole source of much of the evidence due to it being the actual crime scene, along with actually being the source of transport and disposal of her body into the river.
I absolutely find it plausible that the attack mainly occured inside her car..not to get too graphic but a single, hard blow to the head would render her incapacitated therefor not trying to flee from the vehicle and attack.. This type of blunt force trauma would be easily accomplished by Todd all alone(especially since IMO the brutal force used is indicative of deep seated anger, resentment and hate)..
From there Todd simply uses the vehicle as the mode of transport to the disposal location(Rock River).. The only true hard labor would be his dragging the body from the vehicle, across the terrain of the side area of this area of the river, and quite literally drag the body into the actual river.. Job accomplished all alone by 5"6, 115lb, Todd Smith.
He drives her vehicle to the spot off the side of the road where he abandoned it and destroys everything that he had on that night/morning.. He IMO even tho small in stature and frame absolutely could have done it all himself with minimal exertion for the most part.. Dragging a body out of a car is quite simple..what is difficult is the opposite of trying to get a body into a car..jmo..getting it out is definitely doable by almost anyone, any size.. From there as described everything else would be doable and there is no indication that the body was thrown out into gteat depths or the middle of the river..jmo
While I have given my opinion on the possibility of involvement to some degree of an accomplice I do not however believe that an accomplice was necessary in order for Todd to have murdered/disposed of Katrina..jmo..
My apologies I attempted to be as non-graphic as I possibly could in attempting to give a possible scenario of how Todd quite easily could have done this completely solo..
All jmo, tho