D4vd's lawyers are coming out swinging in the preliminary hearing of Celeste Rivas' murder case ... and they're taking aim at LAPD's criminalists.

On Thursday, D4vd's defense attorney, Blair Berk, questioned criminalist Lauren Wallace, who had previously testified about the presence of possible blood evidence in his garage ... specifically asking about the 2 chainsaws they found.

Wallace explained that they didn't swab the chainsaws for touch DNA, considering the presumptive blood testing on the power tools had come back negative.

She added that it didn't make sense to test for D4vd's DNA in the home since he lived there, saying his profile would be all over the place.

But Berk came back swinging, pointing out that multiple people lived in the home, not just D4vd.

Wallace said she was aware of this -- and under Berk's questioning, she also testified they found jugs of fake blood D4vd had used for merch.

As you know, D4vd's been charged with murdering Celeste, after her body was found back in September, dismembered in the front trunk of the Tesla registered in his name.

Prosecutors believe D4vd killed 14-year-old Celeste because she threatened to reveal their romantic relationship. The artist has pleaded not guilty to the charges.

At the end of this preliminary hearing, the judge will determine if there is enough evidence for D4vd to stand trial.