35 birds were taken for testing by North Wales Police Rural Crime Team who now believe they have a possible explanation for the deaths.
They said it is "highly likely" the starlings died whilst trying to avoid a bird of prey, with "the rear of the group not pulling up in time and striking the ground."
One of the dead birds had a ring on its left leg that was traced to Lithuania, meaning the bird was ringed 1662km away from Anglesey.
The birds were originally discovered by Hannah Stevens who said she had seen the "massive flock" flying overhead before landing and appearing to eat something in the road.
North Wales Police Rural Crime Team took some of the birds away for toxicology and post mortem tests to determine what was behind the mysterious incident.
Preliminary tests for bird flu carried out by Defra came back negative and indicated death from trauma and internal bleeding due to impact with the ground.
Now further tests carried out by the Animal and Plant Health Agency have been carried out supporting the theory that severe trauma from falling onto the road was the cause of death.
The have also said it is "highly likely" that the starlings hit the road because they were trying to avoid a bird of prey but the rear of the flock did not manage to pull up in time.
A full toxicology has still not yet been completed.
One of the creatures had a ring on its leg that was attached in Lithuania.
Some starlings will fly west from Eastern Europe during the winter in search of food and then return in the spring.