Electron spin resonance and transmission electron microscopy results are reported that confirm the presence of a microcrystalline as well as an amorphous phase in thin boron nitride films grown by plasma assisted chemical vapor deposition. Line broadening effects in hydrogenated and deuterated samples indicate that a broad central line can be associated with dangling bonds in the amorphous phase, whereas a four-line spectrum and a ten-line spectrum can be associated with paramagnetic boron defect centers located in the microcrystalline phase. The dangling bond concentration is ten times the concentration of the one-boron defects. The hyperfine coupling constant for the one-boron center in the cubic microcrystalline regions is only 20% of the previously reported value for a similar center in hexagonal boron nitride. The relative concentrations of the dangling bonds, the one-boron centers and the three-boron centers depend on the exact plasma conditions used to form the thin films.