Not likely (at least in humans) but possible. Investigate "Vitamin B toxicity". If death occurred shortly after an injection, it is more likely the injection itself (not the injected material) was to blame - e.g. it injection was into an organ, artery, major venous vessel, etc.
I think it's more likely that your turtle was given vitamin a,d,e. That is the most commonly used vitamin injection. This combination of vitamins is very much over-used and not necessary.
This is what the Tortoise Trust has to say about the B vitamins:
VITAMIN-B COMPLEX
The B-complex vitamins are water soluble and excesses are excreted in the urine. Vitamin B1, thiamine, is a regulator in the carbohydrate metabolism; Vitamin B2, riboflavin, is a co-enzyme in energy release and interacts with vitamin B6 and vitamin B12; Vitamin B3, niacin, is also crucial to the energy metabolism and is often obtained by converting the amino-acid tryptophan - this process requires the presence of thiamine, riboflavin and pyridoxine; Vitamin B6, pyridoxine, is involved in energy conversion from glycogen and in the synthesis of haemoglobin and antibodies; Vitamin B12 interacts with folic acid to govern the production of red blood cells. A deficiency causes pernicious anaemia and neurological symptoms. This vitamin is only produced within the gastro-intestinal tract when various micro-organisms act upon trace level cobalt. Deficiencies can occur following malabsorbtion syndrome or as a consequence of severe parasite infestations. The B-complex is just that. A matrix of interacting and inter-dependant compounds.
I'm so sorry to hear about your turtle. My understanding concurs with Yvonne's post from the tortoise table. I had always heard that excess vit B is simply excreted in urine and wouldn't damage liver,kidneys, etc the way vitamins like "D" can. I can't imagine how a healthy turtle would suddenly die 12 hrs after receiving the shot...something is up? Weird-SAD Mystery!