D4vd Murder Arrest Indicates Problems with Prosecution Case

8:39 AM PT -- A law enforcement source tells TMZ ... this was an investigative grand jury and not one designed to indict anyone. But why did the LAPD say they were presenting the case to the D.A. on Monday if the D.A. was in charge of the grand jury investigation?

D4vd's arrest was dramatic for sure, but there's something underlying it that screams something is up with the prosecution's case ... it may not be as solid as people think.

The LAPD arrested D4vd late Thursday and quickly put out a statement that they would present the case to the D.A. on Monday. Here's the thing ... the D.A.'s office already had the case ... they had it for months.

Deputy D.A. Beth Silverman has been presenting evidence to an L.A. County Grand Jury since November, and it seemed by all accounts this was more than an investigative grand jury ... it was a grand jury convened to indict D4vd for the alleged murder of Celeste Rivas. If the grand jury heard all this evidence, wouldn't it make sense for it to indict?

So saying the case would be presented to the D.A. doesn't make sense. The D.A. had the power to file charges and then arrest D4vd, not vice versa.

One thing is clear -- cause of death may end up being the centerpiece of the trial. We know the Medical Examiner had enormous trouble in attempting to determine cause of death, because of the condition of Celeste's body. We do not know if the M.E. has actually determined cause of death or whether the conclusion was "undetermined." Without a clear cause of death -- was it homicide, an accidental OD, etc -- it becomes a weapon for the defense.

Although the defense has said D4vd did not murder Celeste, nor was he the cause of her death, he may have known something about how she ended up in his car. But even if he knew how she ended up in his trunk, it's not proof in and of itself he murdered her.