By Walt Hunter

PHILADELPHIA (CBS) – Fifty-three drug dealers, convicted of selling everything from “crack” cocaine to heroin, have been thrown out by a Philadelphia judge, because testimony and actions of an allegedly corrupt cop may have tainted the cases.

The convictions are among 900 cases, going back to 2002, involving former narcotics officer Jeffrey Walker. Walker, who was arrested last May, has been indicted by a federal grand jury for allegedly attempting to rob drug dealers.

Public Defender Bradley Bridge saying people were wrongly convicted and some sent to prison is also moving that 100 others, convicted in cases involving Walker, also have their convictions dropped.

Assistant District Attorney Robin Godfrey, explaining she was “disappointed” about the convictions being dropped, explained, ”The vast majority entered guilty pleas and we are not, in any way, conceding their innocence.”

Bridges says it very possible hundreds of other convictions involving not only Walker, but other officers, may also be thrown out. The public defender says the root of the problem is that officers are permitted to work too long in narcotics without being rotated to other duties.

“They cannot hang around money or drugs for too long, before you are corrupted by the process.”

Bridge says he hopes to get 10 of the drug dealers, who are still in prison, released as soon as possible.

There is still no estimate of how much it cost to investigate, arrest and successfully prosecute the dealers, whose convictions have now been thrown out.