This is hard to describe, and without having been to the airport before, it's hard to believe as well. I offered speculation before and will again. I've taken off during the day, and at dusk from Catalina more than once. It is a crowned runway, and there is a very credible visual perception that the runway ends only 400-700 feet in front of you. With the landing lights on the plane shining in the immediate forefront, the false image is even more reinforced. It causes pilots, including me to lift off early in the TO run without sufficient climb speed.
In the case of a single pilot in a decently powered plane, the plane will typically climb in ground effect enough to speed through the back side of the power curve(reverse command). In a heavy loaded plane, on a hot day, I'm speculating that the pilot pulled it off green, just as he was viewing the visual 'end' of the runway approaching and flew in ground effect in reverse command region. No amount of back pressure on the control was going to make the plane go any faster, or climb. The plane remained in static flight, in ground effect without climb or speed increase right off the actual end of the runway, where it still failed to climb or increase speed, and now, the ground effect off the west end of the runway is gone, and there was insufficient lift to maintain altitude, and directional control.
I'm not conversant in the Baron, but I believe the right engine is always the critical one, thus leading to the mild turn to the right, descending into terrain.
The solution at Catalina is to 'fly the numbers'. If T/O rotate speed is XX knots do NOT rotate before XX speed is reached. It's quite unnerving to see the runway false 'end' approaching as the plane continues to travel and there is NO visible terrain to the west until the actual end of the runway passes under the plane rather abruptly. Adding to this, the T/O run to the west is a 2deg upslope, in addition to the crown. Thus, if there is any onshore breeze or wind, the plane tends to be seen as accelerating much slower than normal. Going uphill, into a light wind, short view runway the natural inclination is to pull back and get the MFer in the air - NOW.
I could be completely wrong, and some other more credible reason will be found. I think they already confirmed both engines operating at impact, but not sure if both were full power with props in T/O position.